Brian,
I assume you are thinking of the one that measures where the fence is?
If so I think your tablesaw and fence will have to be of very high quality and repeatability to warrant the trust that you will inevitably tend put into the scale reading.
My first thought was that you might have been thinking of using the wixey thicknesser scale to show the blade height. This to me would be very useful function but difficult to engineer such that you could read the scale and get it accurate due to the blade moving on an arc and the scale being linear.
I use digital readout on my metal working machines but those use remote scales with cables to the readout and are very useful. In fact when I had a recent failure of one scale, I realised how much I depend on it and how I'd almost forgotten how to take account of leadscrew backlash in the 20 years the scale had been in use.
Bob