Timegrapher

 

A timegrapher is an instrument that can tell you how accurate your watch is by checking its beat rate, amplitude, and beat error.

A timegrapher is a device that tells you more than just the accuracy of a watch. Through the built-in microphone, it picks up the ticks and tocks of the watch and calculates indicators of the general health of the movement. So a functional timegrapher gives you many useful pieces of information that you can use to determine the condition of the movement.

Parameters - Below are important points to understand before using timegrapher.

Beats per Hour (BPH) or Vibrations per Hour (VPH)

The top-line statistic when describing a mechanical watch movement is the bph/vph. In other words, the number of times the balance wheel will swing half a rotation over the course of sixty minutes. Watches with a high bph, like the Zenith El Premiero at 36,000 bph, tend to be more accurate, with a smoother movement of the second hand, but potentially require more service due to the higher amount of wear it generates. Watches with a lower BPH, like Rolex 1675 at 19,800 bph, have a jumpier seconds hand, slightly less accuracy, but anecdotally require less maintenance over time.

Note: Make sure your watch is mostly wound before testing.

Standard bph ratings

• 14,400 bph = 4 beats per second
• 18,000 bph = 5 beats per second
• 21,600 bph = 6 beats per second
• 28,800 bph = 8 beats per second
• 36,600 bph = 10 beats per second

The popular middle ground these days is 28,800 bph: a good mix of accuracy and durability, and the frequency chosen for the Valjoux 7750, ETA 2824-2 and Unitas 6497, three of the most produced watch movements on the planet, used by nearly every watch company that isn't a complete in-house manufacture.

While good to know the different bph ratings, the timegrapher is pretty spot on at auto-detecting the bph of any watch you put on it. You can program it yourself in the menu, but there isn't much of a reason to unless you have a highly custom movement or it isn't detecting correctly.

Lift Angle

The other thing you'll want to know about your movement is the lift angle. This is the angle the balance passes through while interacting with the pallet fork. The reason you need to input this into the Timegrapher is so that you can calculate the amplitude, which I'll touch on soon. A handy site for finding out the lift angle of your movement can be found here.

Most modern watches have a lift angle of 52 degrees. Generally lift angles range from 44 to 58 degrees. Some other settings are present, for instance the new Omega Co-Axial movement angle is 30 degrees.

• Beat rate: This tells you the rate of the movement. The number is how many seconds per day your watch is running ahead or behind. So, if it says +3s/d, that means the watch gains 3 second per day. 
• Amplitude: This informs you about the health of the movement, specifically by telling you how much rotation (arc) there is in the balance wheel swing. A healthy movement should, at full wound, have a high amplitude, in the range of 280-320. Amplitude is higher when a watch is lying flat and usually falls when the watch is in a vertical position, due to increased friction. Amplitude can also fall as the watch winds down and the mainspring delivers less power.
  Amplitude is a good indicator of the movements health and if is too high or too low, or that changes too much in different positions, can indicate a problem with the movement.
• Beat error: This figure is a bit abstract to understand, but simply put, it’s the time difference between the “tick" and the “tock”. Normally they should be of equal length, but if the balance wheel swings more in one direction and less in the other, one tick will be longer than one tock. This does not affect the accuracy of the watch unless in extreme cases, but in the long run, beat error can cause uneven wear. A high beat error prevents the watch from self starting i.e. it does not start running by itself when wound from a unwound state, and requires you to swing the watch to start running. An exceedingly high beat error, on the other hand, can cause a problem called “rebanking” or even stop a movement.