In the 1970s, Certina had a problem. There were already watches that were sealed and at low pressure to minimize oxidation of the gears and lubricating oils, but they were less accurate than other watches. Moreover, they were impossible to adjust while they were still sealed.
So, Certina sought a way to adjust a fully sealed watch. And this is what they came up with.
Certina put two bimetallic strips on either side of a regulation point, when heated, the bi-metaltic strips would push on the regulation point, adjusting the speed of oscillation.
You may be familiar with bimetallic strips from older-style thermostats. They are exactly what they sound like. A strip of two metals, joined together. Because they are not the same, the metals expand differently when heat is applied, and the metal curves. For a thermostat, it typically has a mercury switch on one side, so when it bends too much in one direction (or unbends) it will turn the heater on or off.
Similarly here, these two bimetallic strips are able to be heated from the outside of the case, and then bend to adjust the oscillation of the movement and make a more accurate timekeeping device.