Girard Perregaux named this model "Casquette", reference number 9931 PF.
Built in is the calibre 396, a battery powered electronic movement with a quartz oscillator, 32,768Hz and a CMOS integrated circuit. The digital display includes hour and minute in a 12 hour display, calibre 397 has a 24 hour display, day and date and seconds. Power comes from two batteries. The watch is accurate to within 1 minute a year. The Casquette was launched in 1976, in three versions, steel, gold plated and Makrolon. Normally the watches were delivered on bracelet, but it was also possible to get the steel and the plated watches on leather strap. The strap has to have two different sized strap ends. One is 22 mm the other one is 25 mm.
Information kindly provided by GIRARD-PERREGAUX SA