Those parts are very small and I found no way to glue the dial back on. If you can dig out the original plastic from the variable resistor, it is easy to adjust with a fine screwdriver. You may be able to make markings on the case with a permanent fine pen. If you have an Ohm meter, you can mark off at 1k increments, otherwise the original resistor is very linear and you can just use even spacings for a working reference.
It was pretty much at this point that I bought a small project box at Radio Shack, a Potentiometer (variable reistor, the one in the One Touch unit is 11k) and beefed up all the wires and made them with banana plugs to fit in the jacks I put on the project box. Much sturdier than the original unit and later I replaced the stylet with a professional one that works much better and the probes are cheaper (on a per unit basis) and don't bend quite so easily. More details at www.NoHair.info