The TMI / Seiko Instruments VD78A is a compact quartz movement designed for hour and minute hands with a separate small-seconds display. It is not an automatic movement, and the small subdial is not a chronograph counter.
TMI's published specification for the VD78A lists a monthly accuracy of less than ±20 seconds under its normal-temperature test condition, an approximate three-year battery life and an SR626SW silver-oxide battery. These are movement specifications; the finished watch's case size, water resistance and crystal depend on the watch built around it.
Official reference: TMI VD78A specification sheet.
VD78 Movement Specifications
| Specification | VD78A |
|---|---|
| Type | Quartz |
| Display | Hour and minute hands with separate small seconds |
| Jewels | 0 |
| Published accuracy | Less than ±20 seconds per month under TMI's normal-temperature test condition |
| Battery | SR626SW |
| Published battery life | Approximately 3 years |
| Operating temperature | -5°C to +50°C |
What Does “Small Seconds” Mean?
Instead of placing the running seconds hand in the center of the dial, the VD78 drives a separate small seconds hand on a subdial. The main center hands show hours and minutes.
This layout can resemble a chronograph at first glance, but the VD78 small-seconds display continuously shows the current seconds. It is not a stopwatch register.
Does the VD78 Need Winding?
No. The VD78 is battery-powered quartz, so it does not require manual or automatic winding. If the watch stops after the battery has reached the end of its service life, battery replacement should follow the watch manufacturer's instructions and any water-resistance service requirements.
How Accurate Is the VD78?
TMI specifies less than ±20 seconds per month at normal temperature under its stated test conditions. That is a movement specification, not a guarantee that every finished watch will show the exact same monthly deviation in all temperatures and conditions.
VD78 in the Thorn T0001
The current Thorn T0001 uses the Japan VD78 small-seconds quartz movement. The watch listing specifies a 37mm case diameter, 44.6mm lug-to-lug length, 9.5mm thickness, domed sapphire crystal and 30m water resistance.
To compare the T0001 Rose Gold option with other warm-finish quartz designs, see our gold-tone watches under $150 guide.
Those finished-watch specifications come from the Thorn product listing, not from the VD78 movement itself. A VD78-powered watch from another brand can use a different case, crystal or water-resistance construction.
VD78 vs Automatic Movements
The VD78 is aimed at a different ownership experience from an automatic calibre. It runs from a battery, does not need winding and uses a small-seconds quartz layout. An automatic movement instead stores energy mechanically and normally requires wrist motion or manual winding.
Neither architecture automatically makes a finished watch “better.” Choose based on the complete watch, maintenance preference, dial layout, case proportions and intended use.
Small seconds at six: quartz or automatic?
The Thorn T0001 Stainless Steel and Militado ML27 Navy Blue & White both display running seconds in a subdial at six. The Thorn uses battery-powered VD78 quartz; the ML27 uses a Seagull ST1701 automatic movement with manual winding. The seconds position alone does not identify the movement type.
Compare the dial details before choosing. The Thorn has concentric tracks and radial hour marks, with blue 12, 3 and 9 numerals. The ML27 has a plain navy center, white outer minute track and a cyan seconds circle. It offers an automatic small-seconds alternative, but the two dial designs differ.
The ML27 lists a 36mm case, 44mm lug-to-lug length and 9.5mm thickness. The listing does not state whether that thickness includes the crystal. Both pictured configurations were available when checked on October 8, 2026; check the selected product option for current stock.
Frequently Asked Questions
Is the VD78 automatic?
No. It is a quartz movement powered by an SR626SW battery.
Is the small subdial a chronograph?
No. On the VD78, the small subdial is the running seconds display.
How long does the VD78 battery last?
TMI publishes an approximate battery life of three years for the movement under its specified conditions.
What watch at Watchdives currently uses VD78?
The current Thorn T0001 37mm quartz dress watch uses the VD78 small-seconds movement. Check the product page for current stock and configuration details.
To compare current watches with an exact 37mm case and quartz movement, browse our 37mm Quartz Watches collection. For broader battery-powered models across other sizes, see all Quartz Watches.
