Sbchev, Good point about leaving it on the setting for any length of time. There are a few no-no's such as NEVER pull on the wrench past the torque setting and never back it off much past the min. setting, loss of calibration can occur if you do either and of course as already mentioned never leave it on a setting.
NEVER, NEVER, NEVER let anyone use your torque wrench unless you are absolutely certain they know how to properly use it. Also NEVER EVER use a tool rental torque wrench because you have no idea how it has been treated and in all probably it has been abused to the max!