This is the ratchet attached to the opposite site of the carrier, as the carrier rides through the retoother it will advance either 1, 2, or 3 teeth. Some ratchets cut 3 sizes, and the knob is adjusted for the proper setting.
So, you always wanted to build handsaws...
Slotting Fixture
Slotting Back
Stamping Teeth
Making a Handle
Assembling the Saw