Wall Clock Beat Problems: Friction Crutch Adjustment, Hermle Service, and Correct Lubrication

A wall clock that keeps stopping despite appearing to run smoothly is one of the most instructive problems a first-time clock repair enthusiast will encounter, because the symptom — pendulum stopping after a few minutes or a few hours — can arise from several distinct causes that each require a different correction. A clock that is out of beat will stop because the escapement receives unequal impulse on the left and right strokes, causing the pendulum to gradually lose amplitude until it no longer has enough energy to trip the pallet and the clock stops. A clock that is correctly in beat but under-powered due to worn pivots, incorrect lubrication, or an unwound mainspring will also stop, but for an entirely different reason. A clock where the hour hand contacts the dial rim, the glass, or the keyhole will stop at a predictable time that corresponds to the point in the rotation where contact occurs. Distinguishing between these causes before attempting corrections is the foundation of effective clock repair, and the diagnostic sequence is the same whether you are working on a Hermle three-train chiming movement or a simple time-only wall clock.

This guide covers the complete diagnostic and service sequence for a wall clock with stopping and beat problems — how to set a friction crutch correctly and what auto-beat mechanisms actually do, how to determine whether the pendulum amplitude indicates adequate power, how to identify physical interference between hands and case components, what correct cleaning procedure looks like for a Hermle or similar weight-driven or spring-driven movement, where oil belongs and where it absolutely does not belong in a clock movement, how to approach plate reassembly without bending pivots, how to evaluate whether a movement needs bushing work beyond what cleaning and lubrication can address, and how the gear train and pendulum length are matched so that the movement runs at the correct rate only with the pendulum it was designed for.

Setting a Wall Clock In Beat

Understanding Beat and Why It Matters

A clock is in beat when the tick and tock intervals are equal — when the pendulum swings the same distance from center to the left before tripping the pallet as it swings to the right. In a clock that is perfectly in beat, the escapement delivers equal impulse to the pendulum on each half-swing, and the pendulum maintains consistent amplitude indefinitely as long as sufficient power is available. A clock that is out of beat delivers more impulse on one side than the other — the favored side pushes the pendulum further than the unfavored side pulls it back, and the pendulum gradually ratchets toward one extreme until it reaches the limit of pallet engagement and stops. The degree to which a clock is out of beat determines how quickly it stops — a clock only slightly out of beat may run for hours before the asymmetric impulse accumulates enough to stop it, while a clock significantly out of beat may stop within minutes of being started.

Verify beat by listening for equal intervals between the tick and the tock. The two sounds should be equally spaced — tick...tock...tick...tock — rather than tick..tock.....tick..tock where one interval is shorter than the other. A clock timing application on a smartphone can measure the beat intervals numerically, removing the subjectivity of listening by ear alone. These applications report beat error as a percentage or in milliseconds, allowing you to determine whether the beat is close enough to acceptable or whether further crutch adjustment is needed. A beat error of zero is ideal; in practice, a beat error of one or two percent is acceptable for most wall clocks and will not cause the pendulum to stop.

Friction Crutch Adjustment

Many wall clock movements — including Korean movements and various European designs — use a friction crutch in which the crutch assembly is mounted on the pallet arbor with enough friction to hold its position during normal operation but loose enough to be nudged by hand to a new position when beat adjustment is needed. This friction fit is what allows beat correction without disassembling the movement — you grip the crutch and rotate it slightly on the arbor in the direction that will center the beat, then release and test. The adjustment is genuinely sensitive: a movement where the pendulum amplitude is small will respond dramatically to even a very small crutch movement, while a movement with healthy amplitude and good power will tolerate a slightly larger adjustment increment before the effect becomes obvious. Work in very small movements, test after each adjustment, and resist the urge to make large corrections because you will overshoot and need to correct in the opposite direction.

The correct adjustment sequence is to stop the pendulum, nudge the crutch one small increment in the correction direction, then start the pendulum by pushing it gently to one side and releasing it. Listen for even beat, check with a timing app if available, and if the beat has improved but is not yet even, stop and adjust again. Continue until the tick and tock intervals are equal and the pendulum swings freely through a healthy arc. Avoid the common mistake of adjusting while the clock is running — small adjustments made while the pendulum is in motion are difficult to control precisely, and the pendulum's inertia at the moment of adjustment will momentarily displace the crutch further than you intended.

Auto-Beat Mechanisms and Their Limitations

Some friction crutch designs are described as self-adjusting or auto-beat, meaning that if the pendulum is released from an extreme position the crutch is supposed to rotate slightly on the arbor until it finds the correct centered position, after which it holds that position by friction. In theory this is elegant; in practice auto-beat mechanisms work correctly only when the friction fit between crutch and arbor is within a very specific range and when the pendulum amplitude is healthy enough to generate sufficient torque to move the crutch. An auto-beat crutch on a movement with marginal power or slightly worn arbor fit may not self-adjust reliably — it will move somewhat but not fully center the beat, requiring manual correction to finish what the auto-beat mechanism started. If you attempt auto-beat setting and the clock does not settle into correct beat after several minutes of running, do not conclude that the mechanism has set correctly and simply wait longer — stop the pendulum and verify beat objectively before assuming the auto-correction has worked.

Power and Pendulum Amplitude Diagnosis

Pendulum Amplitude as a Power Indicator

Pendulum amplitude — the total arc through which the pendulum swings from one extreme to the other — is one of the most useful indicators of whether a movement has sufficient power to run reliably. A movement with healthy power and a correctly adjusted escapement will drive the pendulum through a wide, vigorous arc. A movement that is under-powered due to worn pivot holes, incorrect lubrication, over-lubrication, or a mainspring that is not fully wound will drive only a narrow arc — enough to keep the escapement tripping but not enough to sustain operation when any additional friction is introduced, such as the drag of a chime train warming up, a slight position change of the clock on the wall, or minor variations in the mainspring output through its winding cycle. The characteristic symptom of marginal power is a clock that runs for a while then stops without any obvious cause — the power reserve was just barely sufficient when conditions were ideal, and any small perturbation pushed it below the threshold needed to sustain oscillation.

Assess pendulum amplitude by observing the full extent of the pendulum swing from a position where you can see both extremes clearly. A healthy amplitude for most wall clock pendulums is a total arc of several inches at the pendulum bob, with the bob swinging well past the edges of the movement case on both sides. A marginally powered clock will show a noticeably shorter arc — the pendulum swings just enough to trip the escapement but does not extend nearly as far as a well-powered clock of the same design. If the amplitude is short and the beat adjustment appears correct, the problem is power rather than beat, and cleaning and lubrication rather than further crutch adjustment is the correct next step.

Leveling the Clock and Its Effect on Beat

A wall clock must be hung level for beat adjustment to be stable. Gravity controls the pendulum's rest position, and if the clock is tilted left or right, the pendulum's natural center line will be offset from the mechanical center of the escapement geometry. The crutch can compensate for this offset through friction adjustment, but any subsequent change in the clock's hanging position — shifting slightly on its hook, being nudged when dusting, or settling as the wall anchor shifts — will change the offset and throw the beat off again. Hang the clock on a level wall using a spirit level or digital level app to verify that the case is truly vertical in both axes before spending time on fine beat adjustment. A clock adjusted for perfect beat while tilted two degrees will go out of beat when rehung correctly, requiring the adjustment to be repeated.

Hand Clearance and Physical Interference

A clock that stops at a predictable time — always at the same point in its rotation, or always when the hands reach the same position — is almost certainly experiencing physical interference between the hands and some part of the case or dial rather than a mechanical movement problem. The hour hand on a wall clock rotates close to the dial surface and in some cases may have been bent slightly upward or downward from its original position, either during manufacture or through previous handling. A hand that is bent slightly too low will contact the dial face during rotation; a hand bent slightly too high will contact the glass or the case bezel if the distance is small enough. The contact point can be surprisingly subtle — a hand that clears by a fraction of a millimeter under normal conditions may contact the dial when the clock has been running for an hour and the lubricant has warmed slightly, changing the dynamic behavior.

Check hand clearance by slowly rotating the hands manually through a full twelve-hour cycle while watching the gap between each hand and the dial surface, the other hands, and the case components. Pay particular attention at the keyhole openings in the case where the hour hand passes — the inner rim of the keyhole is a specific interference point on some wall clock designs where the hand can catch if it is slightly out of plane. Correct minor hand plane problems by gently bending the hand at its collet — using a smooth tool that contacts the hand near its center rather than at the tip — to restore the correct clearance across the full rotation. After any hand adjustment, rotate manually through the full cycle again before running the clock under power to confirm clearance is maintained throughout.

Cleaning a Hermle Three-Train Movement

When Cleaning Is Necessary

A Hermle 1051 or similar three-train wall clock movement that has been in service for more than five years, or that has been stored without running for an extended period, almost certainly needs cleaning and lubrication before it can be expected to run reliably regardless of how good it looks externally. Old clock oil does not simply evaporate — it oxidizes and polymerizes over time, forming a viscous residue that increases friction at every pivot hole it occupies. A movement that was correctly lubricated ten years ago and then stored will have this gummy residue at every pivot, which explains why a movement can look clean, have visibly clean gear teeth, and still run poorly or stop unpredictably. The residue is not visible without magnification but is detectable by feel — pivots that should spin freely with almost no resistance will show a slight drag that becomes a significant energy drain when multiplied across all pivot holes in the three trains.

The practical test for whether cleaning is needed is whether the movement runs correctly after beat adjustment and hand clearance have been addressed. If the clock still stops, or runs with a narrow pendulum arc that suggests marginal power, or requires the beat to be readjusted repeatedly because it drifts, cleaning and fresh lubrication are the correct next step. Do not attempt to lubricate a dirty movement by adding fresh oil over old — new oil added to gummy old oil becomes part of the contamination and provides no lasting benefit. Complete cleaning followed by correct lubrication is the only approach that restores a movement to reliable service.

Disassembly and Cleaning Procedure

Before disassembling a Hermle three-train movement, let down the mainspring power on all three trains completely to remove the stored energy that would otherwise cause dangerous uncontrolled unwinding during disassembly. Use an appropriate clock key to hold the winding arbor while releasing the click, then allow the spring to unwind under control by slowly releasing the key through many small increments until the train runs freely with no spring tension. Never attempt to disassemble a wound spring-driven clock — the energy stored in a wound mainspring is substantial and can cause serious injury or movement damage if released suddenly. With all three trains let down, photograph the movement from multiple angles before removing any components, paying particular attention to the positions of the chime and strike detent levers, the count wheel or warning wheel positions, and the relationship between the motion work components.

Clean the plates, wheels, pinions, and arbors using an appropriate clock cleaning solution — commercial clock cleaning solution, or a warm solution of dish soap and water followed by a clean water rinse — with a soft brush and peg wood for the pivot holes. Peg wood is cut to a point and inserted into each pivot hole, twisted to lift out old oil residue, and recut to a clean point before moving to the next hole. This step is important because a pivot hole that appears clean after washing may still have a thin film of old lubricant in the bore that will contaminate fresh oil applied during reassembly. After cleaning, dry the components thoroughly — a low-temperature oven at approximately 150-170 degrees Fahrenheit for a few minutes is effective for removing moisture from pivot holes without damaging the brass. Allow parts to cool completely before applying lubricant.

Correct Lubrication of Clock Movements

Where Oil Belongs and Where It Does Not

Correct lubrication is one of the most consequential skills in clock repair, and the most common mistake made by inexperienced technicians is applying oil to surfaces where it does not belong. The only surfaces in a clock movement that require liquid clock oil are the pivot holes — the small holes in the plates and cocks where the arbor pivots rotate — and the escapement contact surfaces between the pallets and the escape wheel teeth. Every other surface in the movement should remain dry. Wheel teeth meshing with pinion leaves do not require lubrication — the geometry of the involute tooth form is designed to minimize sliding friction, and oil applied to wheel teeth will migrate to adjacent components where it is not wanted, attract dust and debris, and form a gummy residue that increases rather than decreases friction over time. Mainsprings receive mainspring grease applied to the spring coils, not liquid oil, and the barrel arbor pivot holes receive liquid oil like any other pivot.

Apply clock oil to pivot holes using a fine oil applicator or a pointed pegwood stick that has been dipped in oil and touched to the pivot hole entrance — the oil will be drawn into the hole by capillary action and distribute itself around the pivot. The correct quantity is a tiny amount: just enough to form a visible oil film at the pivot hole entrance without pooling or running. Over-lubrication is a serious problem in clock repair — excess oil migrates from pivot holes onto wheel teeth, dial components, and suspension spring surfaces where it does not belong and where its eventual oxidation causes exactly the friction problems that correct lubrication was intended to prevent. A movement that was over-oiled and then stored will typically have visible oil residue on the bottom of the case and on surfaces nowhere near the pivot holes, which is a diagnostic indicator of improper previous service.

Correct Oil Types for Different Applications

Clock oil is not a single substance — different applications within a clock movement require different viscosities and formulations. Pivot holes in the time train and strike train receive a light clock oil of appropriate viscosity for the pivot diameter — finer pivots require lighter oil while heavier pivots can use a slightly thicker formulation. Escapement pallet faces receive a dedicated escapement oil that is formulated to maintain its viscosity and film strength under the specific contact pressures and sliding velocities of pallet-to-escape-wheel interaction. Mainspring coils receive mainspring grease — a heavier lubricant that stays in contact with the spring coils rather than migrating away under centrifugal force as the barrel rotates. Using the wrong lubricant type — such as household 3-In-1 oil on clock pivots — creates problems because these oils are not formulated for the thin films and small quantities appropriate to clock pivot applications and will oxidize and gum up more rapidly than purpose-made clock lubricants.

The specific oils used by professional clock repair technicians are available from clock supply houses and are not expensive relative to the cost of the service interval they protect. Investing in correct lubricants is one of the most practical things a beginning clock repair enthusiast can do — a correctly cleaned and lubricated movement with appropriate lubricants will run reliably for many years, while a movement serviced with inappropriate household oils will require retreatment within a year or two. Keep oils sealed and stored away from light and heat to maintain their viscosity and prevent oxidation between uses.

Reassembling a Three-Train Movement Without Bending Pivots

Plate Reassembly Technique

Reassembling a Hermle three-train movement — or any multi-train plate movement — is the step that most frequently produces bent or broken pivots in the hands of less experienced technicians, because the pivots of multiple wheels must simultaneously enter their corresponding holes in the top plate as it is lowered onto the bottom plate. A pivot that is not correctly aligned with its hole will be forced sideways by the descending plate and bent or snapped if the plate is tightened before the misalignment is discovered. The correct technique is to work incrementally: place all wheels in their correct positions in the bottom plate, then lower the top plate very gradually while using illumination from the side to observe each pivot as it approaches its hole. Stop as soon as any resistance is felt, identify which pivot is not seated, use a fine pointed tool to guide it into alignment, and continue lowering only after confirming that pivot is correctly entered.

Start with the plate nuts finger-tight only, never fully tightened, until every pivot is confirmed seated in its hole. The plate should descend evenly without any tendency to tilt — if one corner is lower than the others, a pivot in that area may be seated on the plate surface rather than in its hole, creating a false impression of progress. Rubber bands wrapped around the assembled plates can help hold everything in position while you check each pivot systematically before tightening. Once all pivots are confirmed seated, tighten the plate nuts gradually in an alternating pattern working around the perimeter of the movement rather than tightening one side fully before the other. Full tightening on one side while the opposite side is still loose can tilt the plate enough to displace pivots that were correctly seated.

Identifying a Bent Pivot After Reassembly

A bent pivot that occurs during reassembly is not always immediately obvious — the wheel may appear to be correctly installed and the plates may close fully, but a slightly bent pivot will show up as increased friction during rotation, a wheel that runs smoothly at some arbor positions and tight at others, or a wheel that refuses to turn freely when rotated by hand after assembly. The diagnostic test is to turn each train slowly by hand after full plate assembly and feel for any position-dependent resistance — smooth rotation through all positions indicates correctly seated pivots, while resistance at specific positions indicates a pivot problem. A pivot that is bent rather than broken will allow the wheel to turn but with increased friction that reduces power delivery to the escapement. Disassemble and inspect any wheel that shows position-dependent resistance before running the movement under spring or weight power.

Evaluating Movement Condition and Bushing Needs

How to Assess Pivot Hole Wear

Pivot hole wear — where the hole has enlarged and become oval from decades of pivot rotation — is the primary wear mechanism in clock movements and the primary cause of the power loss that makes a movement unreliable after many years of service. As a pivot hole wears, the arbor runs off-center at the worn position, which changes the gear mesh depth between wheels and pinions in a way that increases friction and reduces power transmission efficiency. Worn pivot holes also allow increased end-shake — axial movement along the arbor — that causes additional friction as the arbor shoulders contact the plate surfaces. A movement with significantly worn pivot holes cannot be restored to reliable service through cleaning and lubrication alone because the geometric errors from the worn holes will persist regardless of how clean the surfaces are.

Assess pivot hole condition by inserting each arbor into its hole and checking for side-play — lateral movement of the pivot within the hole. A correctly fitting pivot hole should allow the pivot to rotate freely but should show minimal side-play when the pivot is moved laterally. A worn hole will show obvious side-play visible to the naked eye when the pivot is moved. Look at each pivot hole under magnification — a round, clean hole with smooth walls indicates acceptable condition, while an oval hole or a hole with visible wear grooves indicates that bushing is needed before the movement can be expected to run reliably. Hermle movements, which are manufactured to good tolerances with proper materials, typically have a service life of twenty to twenty-five years before pivot holes reach the point where bushing is needed — a movement significantly older than this or one that has been run without correct lubrication will likely need bushing work.

Bushing as a Skill to Develop Progressively

Installing bushings — press-fitting small brass tubes into enlarged pivot holes to restore correct pivot fit — requires a bushing press or staking tool, appropriate drill bits sized to the replacement bushing outside diameter, and practice in selecting the correct bushing size for each application. It is a fundamental skill in professional clock repair but one that requires dedicated tools and practice to execute correctly. Attempting bushing work without the correct tools risks drilling off-center, installing bushings that are the wrong size, or damaging the plate around the hole. The practical advice for a clock repair enthusiast developing their skills is to become comfortable with disassembly, cleaning, lubrication, and reassembly on simpler single-train movements before attempting bushing work on a complex three-train chiming movement. Each skill level builds on the previous, and the added complexity of a three-train movement with chime and strike sequencing creates enough variables that adding bushing work before basic service skills are solid significantly increases the chance of a setback.

When bushing work is clearly needed but falls outside current capability, professional service is the correct answer rather than running a worn movement indefinitely. A worn movement that is continually run accelerates its own deterioration — each hour of operation with worn pivot holes causes additional wear that makes eventual bushing work more extensive and more expensive. If a movement is worth repairing at all, it is worth having bushed correctly when bushing is needed rather than delaying and allowing the wear to progress further.

The Hermle 1051 Movement Specifically

Movement Identification and Pendulum Matching

The Hermle 1051-030 series is a three-train spring-driven chiming movement produced in multiple variants distinguished by the pendulum length they are designed to regulate. The code stamped on the rear plate of the movement includes the model number and a suffix indicating the rated pendulum length — 030 indicates a specific beat rate that corresponds to a specific pendulum length, and using a pendulum of different length will cause the clock to run at the wrong rate. A movement and pendulum that are not matched will produce a clock that either cannot keep correct time even with the bob at its lowest position, or one that gains dramatically because the pendulum is too short for the movement's gear train ratio. When sourcing a replacement movement or a parts movement, matching the complete model number including the pendulum length suffix is essential — a 1051-030 with a 45cm pendulum is not interchangeable with a 1051-031 with a different rated pendulum length even though the movements appear identical externally.

The date code stamped alongside the model number on Hermle movements encodes the year of manufacture and is a useful indicator of the movement's age and likely service history. Movements manufactured more than twenty years ago are candidates for bushing work regardless of how well they appear to run on first inspection, because the pivot hole wear that reduces reliability develops gradually and may not be apparent until the movement is under full load for an extended period. A movement that passes a short bench test but stops after a few days of running under the full chime and strike load is showing marginal pivot hole condition that short testing did not reveal.

Chime and Strike Train Sequencing After Service

Reassembling a Hermle three-train chiming movement correctly requires not only that all pivots be correctly seated and all wheels correctly meshed, but that the chime and strike trains be correctly phased relative to the motion work so that the chime sounds at the correct quarter-hour positions and the strike fires at the correct hour count. This sequencing is controlled by the positions of specific wheels and levers at the moment of reassembly, and incorrect sequencing will cause the chime to fire at the wrong time, the strike to produce wrong counts, or the chime to lock up in a position where it prevents the time train from advancing. Photographs taken before disassembly of the chime and strike train lever positions, count wheel or warning wheel positions, and the motion work are invaluable references during reassembly — without these references, correct sequencing requires either detailed knowledge of how the mechanism works or a process of trial-and-error disassembly and reassembly until the correct phasing is found.

The manufacturer's parts diagram — available from resources such as Cousins UK for many Hermle calibers — identifies each part by number and shows the assembly relationships that must be maintained for correct operation. Consulting this diagram before disassembly allows you to understand the mechanism well enough to record the correct reference positions of each component before they are disturbed. A parts diagram does not substitute for understanding how the mechanism works, but it provides the component identification and assembly reference needed to approach reassembly systematically rather than by trial and error.

FAQs

Why does my wall clock keep stopping even though it's in beat?

A clock that stops despite being correctly in beat is almost always under-powered. Insufficient power to sustain pendulum oscillation can result from old dried oil creating friction at pivot holes, worn pivot holes that have enlarged and allow arbors to run off-center, incorrect lubrication with household oils that have gummed up, a mainspring that is not fully wound, or physical interference between hands and case components that stops the clock at a specific position in its rotation. Check hand clearance first since this is easy to verify, then assess pendulum amplitude — a wide vigorous arc indicates adequate power while a short narrow arc indicates insufficient power requiring cleaning and lubrication.

What is a friction crutch and how do I adjust it?

A friction crutch is a crutch assembly mounted on the pallet arbor with a friction fit that allows the crutch to be rotated to a new position by hand and then holds that position during normal operation. It provides a convenient beat adjustment mechanism — if the clock is out of beat, the crutch is nudged slightly in the direction that will center the beat, and the friction fit holds the new position. Adjust in very small increments, test after each adjustment, and verify beat with a timing application rather than by ear alone if the movement is sensitive to small beat errors. Do not adjust while the pendulum is in motion — stop the pendulum, nudge the crutch, and restart to evaluate the change.

Should I oil the wheel teeth in my clock movement?

No — wheel teeth meshing with pinion leaves should not be lubricated. The involute tooth geometry is designed to minimize sliding friction and the teeth run well dry. Oil applied to wheel teeth migrates to surrounding components where it is not wanted, attracts dust and debris, and eventually oxidizes into a gummy residue that increases friction. Oil belongs only at pivot holes and on escapement pallet contact surfaces. Mainsprings receive mainspring grease applied to the spring coils, not liquid oil. Applying oil to wheel teeth is a common mistake that causes long-term problems and requires cleaning to correct.

What is the correct way to clean a Hermle movement?

Let down all mainspring power before disassembling. Photograph the movement thoroughly before removing any components, paying attention to chime and strike lever positions. Clean all metal components in appropriate clock cleaning solution or warm soapy water with a soft brush, peg out all pivot holes with pointed pegwood to remove old oil residue, rinse thoroughly, and dry in a low-temperature oven at approximately 150-170 degrees Fahrenheit. Do not clean mainsprings with the same solution used for brass components — remove springs from barrels separately and lubricate with mainspring grease before reinstalling. Apply fresh clock oil only to pivot holes and escapement pallet contact surfaces after reassembly, using the correct oil type for each application and applying only a tiny amount per pivot hole.

How do I avoid bending pivots during movement reassembly?

Work incrementally with the top plate lowered slowly and the plate nuts only finger-tight throughout assembly. Use side lighting to observe each pivot as it approaches its hole, and stop immediately if any resistance is felt before identifying the misaligned pivot and guiding it into position. Never force the plate down against resistance. Tighten plate nuts gradually in an alternating pattern around the perimeter only after all pivots are confirmed seated in their holes. After full assembly, rotate each train by hand through multiple revolutions feeling for position-dependent resistance that indicates a bent pivot, and disassemble to inspect any wheel showing such resistance before running the movement under power.

How do I know if my Hermle movement needs bushings?

Check each pivot hole for side-play by inserting the arbor and moving it laterally within the hole — correct fit shows minimal lateral movement while a worn hole shows obvious visible play. Look at the holes under magnification for oval deformation or wear grooves. A Hermle movement more than twenty years old, or one that has been run without correct lubrication, is a candidate for bushing work even without obvious wear symptoms because pivot hole deterioration develops gradually. A movement that passes a short bench test but stops after several days under full chime and strike load is showing marginal pivot hole condition that bushing work will correct.

Does the pendulum length matter for my specific Hermle movement?

Yes — each Hermle movement variant is designed around a specific pendulum length, and the gear train ratio is matched to the beat rate of that specific pendulum. Using a pendulum that is too short will cause the clock to run significantly fast because the shorter pendulum swings faster than the gear train was designed to accommodate. Using a pendulum that is too long will cause the clock to run slow. The pendulum length rating is encoded in the model number on the rear plate — match the complete model number including the pendulum length suffix when sourcing a replacement pendulum or a replacement movement to ensure the pendulum and movement are correctly matched.