Well, I might be barking up the wrong tree here, but if it is a bog standard Digimatic the origin setting is electronic. If you take out the battery and replace it, the first display after it wakes up shows all zeroes, and a flashing P. Twiddling the thimble doesn't change the display. Set the micrometer to zero (setting block or whatever) and press "Origin". Now the "P" disappears and the display responds to movement of the thimble.
You can do the same without removing the battery by pressing and holding "Origin" for about three seconds. This brings on the flashing P and sets the display to frozen zeros. Pressing origin a second time (briefly) removes the flashing P and sets the micrometer working as a measuring device.
I googled the part number 293 etc but couldn't find a close up enough photo to decide if it was different from the standard digimatic. If this doesn't make sense my apologies for leading you up the garden path. If so Can you up-load a photo of the display and controls we can see what you are playing for?
Best rgds Simon