Denis, if that reads 50.0806, the bulletin above points to 1200 rotations/mile...If 50.0804, its for 1610 speedos. But both show for the DS1 (assuming the '058 means the DS1).
Claus, calibrating the speedo is one thing, getting the odometer to count correctly will take the right worm drive gears in the speedo. I have no idea if that is easy to sort, even though they are easy to swap....As you'd guess, Fiats used the same basic mechanism around this time (fiat 850) but 1690g/m (revolutions per mile...really meaning rotations per rotation!) so may be very close to this pic I have of a metric speedo (1.67Msomething....Pantera or Longchamp or...?).
If your speedo is way off (30% no matter what real speed you are going), its probably wrong drive gearing. If just offset (10mph slow whatever the speed) its just a bump of the needle...Lee
