Compare Seiko movements

Choose this comparison by the function you want to see and use: a date, day-date, open heart, second time zone or chronograph. It compares five TMI calibres by function. For the calendar-only decision, use the dedicated NH35 vs NH36 comparison.

Which movement suits each use?

The calendar layouts in the first two rows belong to the movement specification. No verified current MedoMods product match for NH36 is included here. The examples below use the other four calibres.

Published TMI specification comparison

The four NH movements share a mechanical measurement vocabulary; VK63A is a quartz chronograph movement and its accuracy is published per month, not per day. TMI's current VK63 documents used here do not publish a frequency in Hz, so the table does not add one.

For NH35A, NH36A and NH38A, the individual 2022 specification sheets state the −20 to +40 seconds/day figure at 23 ± 2 °C with a 20-second test. Separately, the 2025 NH3 guide describes a static check 10–60 minutes after full winding in dial-up, 9-o'clock-up and 6-o'clock-up positions, with no active calendar function; it does not specify a temperature. Those are separate published conditions, not one combined test of a finished watch.

Start with the display you need

Choose NH35A when the dial calls for a date. Choose NH36A only when day and date are both required by that dial. The NH35 vs NH36 comparison keeps that close pair focused on its calendar choice.

Choose NH38A when the visible opening in the dial is the point of the watch. Its three-hand open-heart specification has no date or day calendar. The NH38 movement guide covers that display in more detail.

Choose NH34A when a central GMT hand and a date are part of the brief. Its first crown position sets the date to the left and the 24-hour hand to the right; the second position sets the time. The product’s bezel, dial scale and hand set still determine how that GMT display is read.

Choose VK63A when the chronograph layout and battery-powered timekeeping fit the design. TMI lists a centre 1/5-second chronograph hand, a minute counter, a small seconds display, a 24-hour indicator and date. It is therefore a different functional choice from the automatic NH movements.

Active MedoMods examples

These current MedoMods examples match their stated calibre:

• MARINER MOD - BLACK uses NH35 automatic movement.
• NAUT MOD - BLACK (OPEN HEART) is an NH38 automatic open-heart example.
• GMT MOD - PEPSI is an NH34 GMT example.
• TONA MOD - PANDA is a VK63 meca-quartz chronograph example.

The movement is one part of the finished watch. Use each product page for the listed case, dial, bracelet and available options before choosing a specific model.

Fit the movement to the complete build

The bare movement diameter and height are reference measurements, not finished-watch dimensions or a universal compatibility verdict. Confirm the dial layout, dial feet, hand fittings, movement holder, winding stem and clearance in the exact case together. A GMT hand, a calendar aperture or an open-heart cut-out changes what the dial must accommodate.

Source basis

Manufacturer figures were retrieved on 9 October 2026 from the TMI NH3 Technical Guide, the NH35A specification, NH36A specification, NH38A specification, TMI catalogue, VK63A specification and VK63 technical guide.

FAQ

Which functions distinguish the movements being compared?

NH35A centres on a date display, NH36A adds day and date, NH38A is the open-heart option, NH34A adds a central GMT hand, and VK63A adds quartz-powered chronograph functions.

Which details apply to the specific watch?

The calibre specifications describe the movement. The product page identifies the movement, display, case and options of the specific MedoMods watch currently offered.

How do movement, display and case work together?

Start with the display you need, then confirm the exact movement, dial layout, hand fittings, movement holder, stem and case dimensions as one complete specification.