The FHF 821 is a flat 17 jewels manual wind movement.
It bases on the caliber 82, with the only difference, that the diameter of the main plate was increased from 10 1/2 to 11 1/2 lignes. The rest of the construction remained the same.
The FHF 821 (Darwil also called it "Darwil 7066"), is a traditional construction with subseconds at "6" and directly driven center minute wheel. This wheel is even ruby beared. Normally, this 17th ruby is not used here, but would have been used as cap jewel for the escapement wheel, but that would have increased the height.
The ring balance, which is (unfortunately) not shock protected already beats with rather modern 21600 A/h and controls a true swiss pallet lever movement, whose pallets are transparent.
The lack of a shock protection in movements of the 60ies was due to makeing it extra flat, which was very popular then. The flat movement construction also reduced the height.
Interestingly, the main plate is stamped as "FHF 82". This is pretty odd, since the FHF 82 uses a different, smaller, main plate!
On the dial side, you see the yoke winding system and the decentral second indication at "6".