I just bought this detent chronometer. Up to now I had believed that "Echappement a Ressort" meant a spring detent chronometer. This is a pivoted detent but the return spring is straight rather than a spiral which I believe is a "bascule". This sprig has the same form as a spring detent but it drives the detent about a pivot. Here are two closer views of the detent arrangement. Here it is with some features called out. The green arrow shows the straight return spring. The red arrow on the lower left points to a peg which position the detent. The other red arrow points to the locking jewel which is a bit hard ot see from this angle. The chronometer is running very nicely so I have not yet worked up the nerve to remove the balance to check out the rest. The maker is very reputable so I believe the marking is legitimate for the time which i estimate to be early 1860' My question is this "Is this what the Swiss meant by "Echappement a Ressort"