Every time I bring a new watch to my watchmaker, he immediately puts it on a stand and shows me as a little blue screen drawing lines, mumbles something, and then gives me an idea of the movement's health. A timing machine, or timegrapher, lets him get a quick snapshot of how a watch is running.
Being someone who likes to really set up shop in my hobbies, and having already started the TZ Watchmaking course, I thought a Timegrapher would be a great addition to my watchmaking desk and a useful tool to determine how well my watches are running. Although not the heavy duty analytics tools real watch repair shops use, for under $200 it is a very worthwhile tool to have around, and its incredibly quick and easy to use. You don't even have to take the back off the watch.
There are a few major benefits to having a Timegrapher. If you like to buy pre-owned, especially vintage watches, its a fast way to get a snapshot of the movement you are dealing with so you know if you need to bring it in for service right away (or return it). If you notice one of your watches struggling or having problems, you can generate some decent ideas as to what is wrong in a few minutes so you can decide where to take it.
Conversely when selling a watch, including the Beats Per Hour (BPH) statistics on your 'For Sale' post shows you to be a more knowledgeable seller who understands what serious buyers want to know. Every time I've asked an eBay seller about the timing of the movement, and they say "runs great, probably under a few minutes a day", its a huge red flag that they don't have knowledge about what they are selling, undermining their credibility and in turn, my interest in buying from them.
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 a 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. Brands including IWC, Bell & Ross, Breitling, Sinn, Hublot and Panerai use these movements as a base upon which to tweak and embellish. They are cheap, reliable, incredibly easy to service (because any watchmaker will know how) and a good base from which to focus on case design and finishing, while keeping prices reasonable.
While good to know the different bph ratings, the Timegrapher I bought 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.
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.
The measure of the amount of rotation in the swing of the balance wheel, in either direction.
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.
Understanding the results
So you've got your timegrapher, you've input the BPH, Amplitude and Lift Angle, and now you want to know what to look for. I'll preface this strongly by saying that a) I am in no way a trained watchmaker and b) the timegrapher only looks at a quick snapshot of the watch, it doesn't give the whole picture. For instance, how it runs when the power reserve is low.
1. Rate - How fast/slow the watch runs in seconds per day.
This is the most basic statistic and will at least let you know how accurate your watch is. If your watch is COSC certified, in order to be in good health it needs to be running between -4 and +6 seconds per day. Otherwise it will depend somewhat on the watch, but with a few exceptions you should consider the following to be a good range of your movement's health. If it is wildly out of these ranges, you should bring it to a watchmaker to get it checked out.
- Excellent - +/- 7 s/d
- Acceptable - +/- 20 s/d
2. Amplitude - the amount of rotation in the swing of the balance wheel
- great : 270-310
- acceptable : 250-270
3. Beat Error - how equal each swing of the balance wheel oscillation is.
- Excellent : 0.0 - 0.5 milliseconds
- Acceptable : 0.6 - 1 milliseconds
For a more in depth course on the measurement of mechanical watch movements, Witschi has put online a very thorough and easy to understand lesson document. Check it out here: Test and Measurement Technology for Mechnical Watches.
Bonus: If you want a video to show you how to use a timegrapher, I really like this guy: http://www.youtube.com/watch?v=lcCKrioYKMo