Seiko (SII/TMI) NH38A

Seiko is a Japanese maker that produces its own mechanical, quartz and Spring Drive movements entirely in-house.

01Specifications

02What these specifications mean

Frequency is how fast the balance wheel swings, counted in vibrations per hour (vph) or in hertz (Hz), where one hertz equals two vibrations. A higher frequency means the escapement divides time into finer slices, so the watch tends to keep a more stable rate and resists small shocks better. It also means the tick the timegrapher hears arrives more often, which the analysis uses to lock onto the beat.

The lift angle is the arc, in degrees, that the balance wheel travels while the pallet fork is engaged and pushing it. A timegrapher cannot see the balance directly; it only hears the tick, so it must be told the lift angle to convert the timing of those ticks into an amplitude reading. Enter the wrong lift angle and the rate stays correct but the amplitude figure is off by several degrees.

The power reserve is how long the movement runs from a full wind until it stops. As the mainspring unwinds its torque falls, amplitude drops and the rate usually drifts, which is why a watch can read differently at full wind versus near the end of its reserve.

03Measuring this caliber with WatchScope

To measure the Seiko (SII/TMI) NH38A, set the lift angle to 53° in WatchScope before you start, so amplitude is computed correctly for this movement. Rest the watch against the phone microphone in a quiet room, pick a position and let the reading settle for a few seconds. For a complete picture, repeat the measurement in several positions.

Frequently asked questions