FEF 21.5"

duplex escapement for jumping second (Fig.3) Due to one pair of rest teeth for each pulse tooth, the second hand changes between a hardly visible step and about one second, thus appears as jumping second. The balance gets only each four beats (once per second) an impulse. It doesn't self start (like in every duplex escapement); the movement neads a twist motion to start. indirect minute, direct second This concept became common again in new designs after 1950.