I am currently stringing with a tension differential of 5 lbs (crosses strung looser). I use full poly. When I get my racket strung on an electronic machine (Wilson Baiardo or Tecnifibre TF8000), I am able to confirm that the tension differential is present by measuring the change in the length of my racket. It is -3 mm. The results have been consistent for different poly strings and different tension setups (48/43 lbs and 45/40 lbs). This is what I want. However, when I get my racket strung on a crank machine (Gamma Progression ST II) by a different operator, the racket length is either unchanged or very slightly longer (+0.5 mm), indicating that the desired tension differential is not present, despite the tensions on the machine being set at 48/43 lbs. What might be the reason(s) for this failure on the crank machine? The crank machine is calibrated and the operator uses the double-pull method.