Unlike today, Heuer used to specialize in far more than watches - to include stopwatches for sports timing, yachting, science and research (like the example here), automotive, aircraft, and far more.
Its stopwatches were designed to measure everything from 1/5th a second to 1/100th of a second, and the example here measures 1/5th a second and was designed for science and research applications.
Per Heuer literature of the era, the 1/5th second stopwatches were most frequently used for measurements in laboratories, research, and sport. Events measured usually were timed events exceeding 10-15 minutes.
Operations are via a central crown, with start, stop, and return to zero by successive depressions of the crown, lending to simple time measurements, for example the duration of chemical reactions, track timing, etc.
1970's Heuer Ref. 403.201 Science & Research Stopwatch w/Box
DIAL: Original Heuer-signed white dial, with original minute and second hands.
CASE: Original 53mm x 67mm steel case in pre-loved condition. Original Heuer caseback, complete with Heuer sticker.
CRYSTAL: Original crystal - no scratches.
MOVEMENT: Original "shockprotected" seven-jewel Heuer manual mechanical movement.
CROWN: Original unsigned stainless-steel crown; original minute and second hand reset pusher.