Making a DRO Question

Last night I was looking on the net and found some pages talking about using
a computer as a DRO. I also found one site with very limited info on an
encoder strip similar to those used in a digital caliper. Does anyone know
of such an encoder strip and can a person make one or buy one and then use a
circuit to give you the readout as opposed to the computer?

The pages I looked at used a string or timing belt and that didn't seem like
it would be to accurate or at least not for long.

Thanks
Stan

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