A lot of digital vernier calipers have a little socket under a cover to plug into a computer. These are usually 4 wire, the correct plugs appear to be unobtainable so take caliper apart and solder direct onto the connector pads. There is a lot of information on the internet with complete instructions and even Arduino programmes, (sketch) to read output. I basically used one of these programmers but altered it a bit to do what I wanted. One interesting thing we found was that the on/off switch on these calipers only turns off the display NOT the whole caliper. That explains why if you haven't used caliper for a while you may find battery flat. DRO is powered (1.4v) into "plug" no battery.
Tacho reads the impulses from an infrared transmitter/receiver LED. That part I had already done as a tacho for my old diesel camper-van.
I will look up some articles and post the URLs hopefully tomorrow