Slarty: Methinks you just got back from lunch at the Turf.... Or was it the Queens around the corner.....

I'm sure there were some printers that always returned the head to a datum point at the end of printing but then you'd need to get lucky in so far as the target needs to be using such a printer.... otherwise the start point is an issue. Now if you could get a very high quality recording you may be able to determine the sound certain letters make..... In that case you have your datum right there.

As you pointed out this is 15 years old...... Lets see if you can do it with a laser printer......