Thanks for that Irvine,
Thats interesting. Re the reader units. Am I correct in thinking that the 4 bit BCD type readers do change the transmitted values when switching between metric and imperial? If that is the case it would be a lot easier to get the reader to do the conversion rather than the top end.
Thank's for the insight into the capacitive sensor operation. I was not aware the bar has a strip pc under the label. That's a bit of a nuisance as my plan was to buy cheap 6" calipers and fit longer bars. making long strip pcb's is not out of the question but I guess that the whole reader accuracy relies on the pitch accuracy if the T and comb? Do you know if the comb fingers are isolated from each other or linked together, its hard to see on the photo. It looks like the Ts are isolated from each other.