Breitling Chronomat is the reference in this note. Start with the case in your hand, not with a listing photo. Turn the watch over and read every engraving before you look at the advertisement. A reference names one case and one dial. Write that reference down, then measure across the bezel and from lug to lug. Those two measurements answer different questions. One is the width people quote. The other is how the watch sits on a wrist. Look at the lugs where they meet the bracelet or the strap. A gap you can rock with a fingernail means the end piece or the spring bar has been changed. Open the clasp and look at the inner fold for wear and for a stamping that does not match the case. The crystal should meet the bezel in an even lip. Chips hide at that lip. The hands should pass one another without rubbing, and the seconds hand should sit above the minute track rather than dive into it. If a date window is present, cycle it and watch the disk sit level. None of these checks require a story about where the watch was cased. They require the watch itself, a ruler, and a few minutes of attention at a desk.
How it differs
Breitling Chronomat carries chronograph pushers. Press each pusher with the same finger and write whether the tension matches. The reset should park the chronograph hand at 12, or you should say how far off it sits. Subdials should be level in their recesses. People change pushers, hands, and bezels on chronographs. Compare the wear on the pusher ends with the wear on the lugs before you decide the whole watch has one age.
What to check on a used piece
What to check on a used Breitling Chronomat starts with the engraving. Then check end-link play, clasp fold, and whether the hands pass each other. There is no price in this note.
Common mods
Common changes on a used chronograph are a replaced hand, a pusher that was swapped, and a bezel that was polished. The subdial layout should still match the reference. If a pusher color does not match its twin, say so.
What people change
On the Breitling Chronomat, people change the bracelet, the case, or the movement.