Deadbeat seconds (jumping seconds)
Deadbeat or jumping seconds is a display in which the seconds hand advances one distinct step each second. In a mechanical watch, a dedicated mechanism produces this movement. One-second steps alone therefore do not prove that a watch is quartz-powered.
A documented example is A. Lange & Söhne's Richard Lange Jumping Seconds. The manufacturer describes 60 jumps per minute, coordinated with a constant-force mechanism. That model also has a separate zero-reset mechanism. These are interacting functions rather than different names for one function.
Distinguish deadbeat seconds from hacking, which pauses the hand during time setting, and from a foudroyante showing fractions of a second with a fast hand. For an older watch, examine hand motion, calibre and documentation together. Video can record the movement, but cannot alone establish the internal construction or rate accuracy.
