Tissot Sideral “Bullhead”

You have to study the pictures to see this watch! It really has many surprising features for a vintage watch from ca 1970. Basically a timer (chronograph/stop watch) that is fixed to a stiff steel bracelet. Pushers at 12 o’clock justifies the term “bullhead”. And then the mysterious scaling of the outer part of the dial and the corresponding markings on the bezel!?