(c): Mars Mountain
ZENITH movement cal. 2531 from somwhere around 1964, 19 jewels manual subsecond movement. Based on cal. 2511, but equipped with a micrometric regulation system and a higher beat rate (21 600 vs 18 000). The power reserve holds a good 50 hours. This watch, model 220 S, is very accurate losing approx. a second per day.
