It is my understanding that the beam types do not go out of calibration. Even if you drop it, or otherwise bend the free arm, a simple straightening so the beam reads "0" and its OK.
The clicker types are easier to use since you don't have to bend your neck at funny angles to see the scale, but calibration can be an issue.

Whenever I do critical work, I set my clicker wrench, clamp the 1/2" drive in a vise and apply pressure at the middle of the hand grip using an electronic scale to measure the force. Then I multiply that force by the distance to the center of the 1/2" drive as a check on the applied torque to make it click. Its a quick and easy way to make sure the calibration is good.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags