Probably the most important thing a stringer can do for their customers is to calibrate their machine regularly. This will ensure consistency in tensioning.
There are a lot of good stringers out there, but those of us that are serious about what we do will always make sure the extras are done too. And there are quite a few extras, one of which is obviously Machine Calibration.
I calibrate my machine once a month, some people do it more often, others don't do it at all. For me it is something that most of my customers will never ask about but it is something I feel I need to do for them.
It means I know the tension they are asking for is the tension they are getting. I also know that it will be the same tension the next time they come back.
Stringing is all about being consistent, whether it is how you weave your strings, the type of knot you use or even how you stencil the rackets.
But the most important factor is having a consistent tension!