The Roamer caliber MST 424 was produced in the 1950’s in Solothurn, Switzerland.
Roamer Watch Company was founded in 1888 and watches are still being made under the Roamer name. The letters MST come from the initials of the founders. They established the Meyer & Studeli movement factory in 1905 and by 1952 they were making watches fully in-house with the name Roamer. On the caliber above, the MST stamp is partially visible behind the balance wheel.