Quick answer
A replica Type XXI 3817 is judged on three points: whether the case profile matches the 42 mm original, whether the subdial layout is correct, and whether the chronograph truly works as a flyback. Most copies get the first one close, miss the second in small details, and fail the third. Check those before you look at anything else.
Know the original first
The Breguet Type XXI ref. 3817 is a 42 mm steel flyback chronograph with a fluted case band, welded lugs held by screw bars, a black dial carrying a 24-hour day and night indicator, small seconds, a chronograph totalizer, and a date window. Water resistance on the original is rated to 100 m. A copy measuring 40 mm, or one with a smooth polished case band, is not a faithful reproduction of this reference.
What to have on hand
- Digital caliper for case diameter, lug-to-lug, and thickness
- 10x loupe for dial printing and case band fluting
- Stopwatch or phone timer for chronograph accuracy
- Bright raking light for brushing and polishing transitions
How to inspect one, step by step
- Measure the case. Diameter should land at 42 mm and thickness near 15 mm. A 12 mm case wears wrong on the wrist.
- Run a fingernail around the fluted case band. The cuts should be even, with no flat spots or burrs.
- Examine the lugs. Screw bars must sit flush, and the lug shape should flare outward from the case instead of dropping straight down.
- Inspect dial printing under the loupe. Subdial rings should be crisp circles and markers should sit at matching heights.
- Verify each subdial function. Small seconds must run continuously, and the 24-hour indicator must sweep once per 24 hours, not once per 12.
- Test the chronograph. Start, stop, and reset ten times. The reset hand must snap to zero every time without drift.
- Test the flyback if the listing claims it. With the chronograph running, press reset once. A real flyback returns to zero and restarts immediately.
- Cycle the date through three full months. It should advance without hanging near midnight.
- Work the crown. Threads should engage over several turns and the crown should screw down without force.
- Track rate over 48 hours or use a timegrapher. A sound automatic movement holds within roughly -10 to +15 seconds per day.
Movement tiers you will encounter
Copies of this reference usually run one of three engines: a modified Valjoux 7750 with an added 24-hour module, a Seagull ST19 hand-wound chronograph, or quartz. The 7750 option gives the right pusher feel and a sweeping chronograph hand. The ST19 is thinner and winds smoothly but carries less rotor weight. Quartz versions tick once per second on the small seconds and lose the mechanical character entirely.
Flaws that justify walking away
- Polished smooth case band instead of fluted
- Subdials printed as flat decals rather than recessed and stepped
- Chronograph resetting to 12 o'clock instead of zero
- Lume fading inside 20 minutes
- Pushers that feel gritty or bind halfway through travel
Wearing and care
Keep the watch out of hot water and steam even with a 100 m rating. Gaskets age on any watch, and a chronograph adds two more case openings. Have gaskets checked yearly if you swim with it. A 7750-based movement wants service about every five years. Store it on a winder or wind it weekly so lubricants stay spread across the pivots.