I have a problem with my 205 TD rear brakes?

The brakes are uneven and this is on a rolling road. the one side is more efficient by as much as 58%!! But the drums are new, shoes changed with drums and cylinders all work. NO leaks, and new brake cables.

I am getting a reading of 58% in the red on the rh side and am looking at the left side to be wrong. IS this right?? OR am I barking up the wrong tree!!

Is there a usual reason for this imbalance?? Car HAS been stood but fronts are within 3% tolerance and Handbrake is 19% out of balance.