Originally Posted by rick
You could just do a millimetre scale around the entire circumference they could then set the zero at what ever point they want and do a simple chart, something like 4.4mm = 50yds or meters, 5.6mm =55yds/mm depending on your choice of measurements. Adjustments for temperature, colour of target, variations in the users eyes and any other variation in the scope could be easily compensated for. You wouldn't need separate index marks for normal and cold temperatures.
Once you know the reading for each distance compensating for variations becomes simple and the more anal ones out there could easily work out distances to the yard.
I did that years ago on my Nikko sidewheel: printed a scale strip and had a lookup chart. The problem was it was too tempting sometimes to round up or down to the nearest mark before
looking up the range. Not normally a big issue but every once in a while that little error added to a yard or two ranging error making a miss high or low.