Jim, Google up the ancient Greek "clepsydra" or water clock. Not a dial of course but I'm thinking by 1810, there had to be not just a concept but also the micro-machining skill among clockmakers to easily fashion this contraption. Or, I'd think it's pretty easy to move a spring-loaded shaft (spring scale is a good example) and "read" the amount of travel of a pointer attached to shaft or simply the opposite end of the shaft against a graduated scale. You could certainly build a big "tuning fork" caliper with this simple "linear" readout in place of the conversion of linear movement to angular movement (circular) of the dial. Pure speculation as I have never seen a W/T gauge from back there around the War of 1812. I'd wager it wouldn't have had a digital readout.
jack
