.... now do not get too excited, this is not a description of how to use a $2 calculator to convert your shop to CNC or even as a substitute for a DRO system but it might have some uses anyway.
The simple calculator which has been around for a few decades is really a pretty nifty device! The bigger ones, which are often the cheaper ones, can be opened and slightly modified to become something quite useful in the shop.
But before opening the poor thing take a moment to play with the keys. For example press the '0','+','1' and '=' keys and the display shows '1' (no suprises there) press the '=' again and it increments to '2' and so on. Your simple calculator is acting as an even more simple counter.
Instead of entering '1' enter some number with a decimal value, for example '0.254' and imagine that each press of the '=' key represents one millimetre in which case the display shows the equivalent in inches.
All very interesting, I am sure [yawn] but how to make use of it....? Open the calculator and locate the connections that go to the '=' key, attach a couple of thin wires and extend those to the outside when putting the cover back on the calculator.
What you use it to count is up to you but dont forget that you can count other than unitary values so, for example, knowing the pitch of your lead screw you could get a direct readout of carriage travel in metric, inches or any other measurement system you prefer.
OK, not all that useful but what did you expect from a pocket calculator?