I am at a customer that is having a repeatability issue with the Y axis. per customer it is not repeating within 0.030" This is a manual CMM

I arrived did probing (69.0 µm) and repeatability test largest error in Y axis at almost 0.001"

Using 40'' step gage. I did my aglinment, set my zero. Measured 1 inch increments. 

My measured lengths were good. After measuring 10 inches i came back to zero point to see what my deviation was it was roughly 0.0001"

I repeated that process at 15 inch and 20 inch. after measuring 15 inches i came back to zero and was still roughly 0.0001" off from zero. 

After measuring 20 inch and coming back i was off 0.015" 

i went back to measure 21 inch mark and i was about 0.015" to the small side.

I repeated that process. measure 22 inch and back to zero. so forth and so on up to 35 inches. by the time i was done. i have a rough total of 0.035 error. Not repeating. is this a scale issue or probe head issue

Probe head is Renishaw PH1 with a TP 20.