I have a Tissot Automatic PR 516 from the early 70s. Time is kept well. Date moves forward correctly but it is the wrong date. I am unable to turn back the date. I am able to turn back the day. Any suggections?

The crown wheel (winder) should have 3 positions, (1) the normal winding position (3) fully out; at this position the watch stops and the time can be adjusted.

(2) This position is between the 1 & 2 and is used to adjust the day and date. If you wish to change the date by winding the crown backwards or forwards.

Since watches can very a little, if turning the crown when in position 2 the date does not change, pull the crown to position 3 and turn the hands until you pass the midnight position, when the date will change and then re-set the time. If you wish to advance the time more than one day, when it changes, wind the crown backwards past the midnight position and then wind it forwards again. Repeat until the correct date is showing and then re-set the time. The exact distance you need to turn the crown to change the date will have to be found by experimenting!