A reference for the watch you own
The battery it takes, the movement inside, its real size on your wrist and the strap that fits the lugs. Every number names the document it comes from, and where two sources disagree you see both.
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Drawn to scale from published sizes, not a photo.Casio F-91W page →
Drawn to scale from published sizes, not a photo.Seiko SRP777 page →
A reference page starts with the answer, then walks the chain: the model points to its movement, the movement to its cell, the lugs to a strap. Three real entries from the data, as their pages open.
Watch · Casio · digital quartz
Inside is Casio module 59311, and it runs on one CR20165 lithium cell, rated by Casio for about 7 years. The band is Casio’s own, sized for wrists of 145–200 mm5. Its lug width is 18 mm7seller listing, held by pins rather than standard spring bars.
Watch · Seiko · automatic diver
The SKX007 runs on the Seiko 7S2613seller listing automatic, so there is no battery to change. Its lugs take a 22 mm1measured strap; the case measures 42.5 mm1measured Sources disagree: measured 42.5 mm / measured 42 mm2 across and 46 mm1measured lug to lug.
Battery · silver oxide button cell
377 is the common name of the SR626SW, a 6.8 mm15 × 2.6 mm15 silver oxide17 cell at 1.55 V15. Seiko lists it as SB-AW15, Citizen as 280-3915. In our data 51 movements and 5 models name it.
Each tool works on the same sourced numbers as the reference pages and shows the result as a drawing to scale, not a score.
Lug-to-lug against your wrist: compact, balanced, at the edge or overhanging.
Balanced — lugs inside the top of the wrist. 46 mm over a ~53 mm wrist top
| Seiko SKX007 | 46 mm L2L | Balanced |
|---|---|---|
| Seiko SNXS79 | 43 mm L2L | Balanced |
| Seiko SRP777 | 48 mm L2L | At the edge |
| Casio F-91W | 38.2 mm L | Compact |
Two to four watches on one centre, to scale, with a 1:1 mode.
Seconds a day against the tolerance its movement is rated for.
Can one cell replace another: size, chemistry and voltage side by side.
CR2032 for CR2025? Same diameter, 0.7 mm taller: the checker sets size, chemistry and voltage side by side before it answers.
The year and month in the six digits on the case back.
652290 on case 7005-8062 reads May 197624. The decade comes from the calibre, so the tool asks for it.
Lug width, strap length and taper for your wrist.
Lug widths across the models in our data (9.1 mm: 1, 16 mm: 2, 18 mm: 10, 19 mm: 7, 20 mm: 65, 21 mm: 3, 22 mm: 47, 23 mm: 4, 27 mm: 1). Integrated bands, like most Casio, are left out.
Also: movement comparison — two calibres field by field.
The same button cell is sold as 377, SR626SW, SB-AW and 280-39. The reference folds 368 printed codes onto the physical sizes they name, with the size and chemistry from the cell makers' datasheets.
| Size | Also sold as | Ø × height | Named by |
|---|---|---|---|
| MT621 | MT621 | 6.818 × 2.1 mm18 | 20 movements · 472 models |
| CR2016 | CR2016 · SB-T11 · 280-206 | 2025 × 1.6 mm25 | 89 movements · 276 models |
| SR621SW | 364 · SB-AG · 280-34 | 6.815 × 2.15 mm15 | 139 movements · 55 models |
| SR927SW | 395 · SB-AP · 280-48 | 9.515 × 2.7 mm15 | 135 movements · 39 models |
| SR920SW | 371 · SB-AN · 280-31 | 9.515 × 2.05 mm15 | 155 movements · 4 models |
| MT920 | MT920 | 9.526 × 2 mm26 | 10 movements · 137 models |
| CR2025 | CR2025 · SB-T14 · 280-205 | 2027 × 2.5 mm27 | 95 movements · 42 models |
| SR726SW | 397 · SB-AL · 280-28 | 7.928 × 2.6 mm28 | 44 movements · 49 models |
“Named by” counts the movements and models in our tables that list the cell — Seiko’s calibre chart, Citizen’s and Casio’s model tables — not sales.
All battery sizes and codes →Movement pages carry what a watchmaker or a modder checks: size and height, beat, reserve, lift angle, hand-hole sizes and where the dial feet sit, each from the maker's sheet.
| Calibre | Diameter | Beat | Jewels | Reserve |
|---|---|---|---|---|
| TMI NH35 | 27.4 mm19 | 21,600 bph29 | 2429 | 41 h20 |
| TMI NH36 | 27.4 mm30 | 21,600 bph29 | 2429 | — |
| Seiko 4R36 | 27.4 mm31 | 21,600 bph32 | 2432 | 41 h32 |
| Seiko 6R35 | 27.4 mm33 | 21,600 bph22 | 2422 | 70 h22 |
| Miyota 8215 | — | 21,600 bph23 | 2123 | 42 h23 |
| Miyota 9015 | — | 28,800 bph34 | 2434 | 42 h34 |
| Sellita SW200-1 | 26 mm35 | 28,800 bph35 | 2635 | 41 h35 |
| ETA 2824-2 | 25.6 mm36 | 28,800 bph36 | 2536 | 42 h36 |
Numbers come from makers’ datasheets, manuals and spec sheets first, then measured reviews, then everything else, labelled. Nothing is averaged and nothing is guessed: a number we cannot source reads “not published”.
Where facts come from
Documents checked · Report a wrong number
