We used to have to calibrate the whole bases torque wrenches, every three months in my shop. Holy crap that was a full time job. PIA they had to saturate in low humidity between 70-80 degrees F for 20 hours, then you could calibrate them. But you can have it in your toolbox in -20 or 130F and use it. Never got that part of it.
CDI makes them for snapon. Best out there. Buy it direct 1/2 the price.
[URL]http://www.cditorque.com/[/URL]