Thanks Jazzcnc I used my digital vernier, which is not a cheap one and is accurate, it has to be when I am working on the lathe or any of the m/c engines I rebuild, I can assure you I did it as you said using the mach3 programme for measurment, I actually did the x axis and a axis three times and did test runs inbetween and the distance it moved was never spot on, it showed the correct distance on the screen but it varied by 0.12mm or near to that each time. Ok did not fully understand the probe, just saw it being used on a urine video and thought ,oh that looks easy, but you know what thought did :-)
I will take you up on your offer of help and will ask later, but ask if you can imagine me as thick, and explain things simply. Or in simple steps.
I was given a downloaded version of Mach3 by the Chinese eBay seller so never got the CD with forerunner and the other test programmes.
I will leave things as metric, having to input different codes to change things at the stage I am at will be a disaster.
All the best
Richard