The lift angle is the angle through which a watch's balance wheel turns while its impulse jewel is in contact with the pallet fork: the moment the escapement gives the balance its push. It is fixed by the calibre's design, and for most modern calibres it lies at around 50°.
Why a timegrapher needs it
A timegrapher hears each beat as a short cluster of sounds. The time from the first to the last of them is how long the balance takes to pass through the lift angle. Knowing that angle and how long each swing lasts, the timegrapher can work out how far the balance swings: its amplitude.
The lift angle only affects amplitude. Rate and beat error come from the timing of the beats themselves, so they are right whatever lift angle is set.
Lift angles of common calibres
| Calibre | Beat rate | Power reserve | Lift angle |
|---|---|---|---|
| Rolex 3000, 3035, 3075, 3085 | 28,800 vph | 42 h | 52° |
| Rolex 3130, 3131, 3132, 3135, 3136, 3155, 3186, 3187 | 28,800 vph | 48 h | 52° |
| Rolex 3175, 3185 | 28,800 vph | 50 h | 52° |
| Rolex 3230, 3235, 3255, 3285 | 28,800 vph | 70 h | 52° |
| ETA 2824-2, 2836-2 | 28,800 vph | 38 h | 50° |
| ETA 2892-A2, 2893-2, 2895-2 | 28,800 vph | 42 h | 50° |
| ETA (Valjoux) 7750, 7753, 7754 | 28,800 vph | 42 h | 50° |
| Sellita SW100, SW240-1, SW260-1, SW279-1, SW400-1 | 28,800 vph | 38 h | 50° |
| Sellita SW200-1, SW220-1 | 28,800 vph | 41 h | 50° |
| Sellita SW300-1, SW330-1 | 28,800 vph | 42 h | 50° |
| Sellita SW215-1 (hand-wound) | 28,800 vph | 42 h | 50° |
| Sellita SW320-1 | 28,800 vph | 48 h | 50° |
| Sellita SW330-2, SW360-1 | 28,800 vph | 56 h | 50° |
| Sellita SW510 M (hand-wound) | 28,800 vph | 58 h | 50° |
| Sellita SW500, SW510, SW600 | 28,800 vph | 62 h | 50° |
| Oris 733 | 28,800 vph | 41 h | 50° |
| Seiko 7S26, 7S36 | 21,600 vph | 41 h | 53° |
| Seiko 4R34, 4R35, 4R36, 4R37, 4R38, 4R39 | 21,600 vph | 41 h | 53° |
| Seiko NH34, NH35, NH38, NH70 | 21,600 vph | 41 h | 53° |
| Seiko 6R15 | 21,600 vph | 50 h | 53° |
| Seiko 6R31, 6R35 | 21,600 vph | 70 h | 53° |
| Seiko 6R54, 6R55, 6R5A, 6R5H, 6R5J | 21,600 vph | 72 h | 53° |
Many brands use these movements under their own calibre names: the Oris 733, for instance, is based on the Sellita SW200-1. When your watch's calibre is based on one of them, the base movement's lift angle is a good starting point.
Setting it in Horology
When you add a watch from Horology's catalog, its calibre comes with it, and the Timegrapher uses that calibre's lift angle where one is published. Otherwise it uses 52°, a common value, and you can set anything from 38° to 60° in the watch's details.
For what amplitude, rate and beat error tell you, see the timegrapher's three numbers.