|Waltham 1908-642 from 1918.|
A fairly rare movement with only 3,000 made in two runs, as an intermediate grade between the -640 and -645, it appears to be a 1908-640 but adjusted to 5 positions rather than 3 and without some of the decoration of the -645. The two runs were mixed Lever Set Railroad watches and Pendant Set Railroad Grade. I have had 3 of these, all pendant set and it is possible that the Pendant set versions were for the UK where Lever Set watches were not popular.
The 17 jewel movement is also adjusted for temperature and possibly isochronism, it has a Swiss lever escapement with a steel escape, Breguet sprung cut compensating balance, double roller and screw micro adjustment.