Unanswered Z axis calibration

so been working bugs out with my printer lately. made some decent progress, down to one last issue. I printed a 20mm calibration cube. it measured 20.01(x)x20.01(y)x20.85(z). is this to minimal difference to attempt to calibrate and if I should, how do I calibrate the z axis?

 

yea, I wasn't sure if that was bout what the printer will do or something I needed to fix. just couldn't stay away from the printer, lol. I seem to have gotten it going though. one of the problems I realized in s3d with pla at least was when the print would start, the cooling fan would shut off pulling the print in all different directions. another was the temps were set too low. even though I would change the temp in the machine controls window. when a print started, the temp would keep dropping. think my eyes are permanently crossed from staring at settings for weeks. cant wait for my e3d to come in tomorrow

 

You don't calibrate the X Y and Z axis, they are a calculated value based on thread pitch and the number of teeth.