I have a 3/8 and 1/2 KD micrometer style torque wrenches that I use daily (building engines). We have a Snap-On caibration unit at the shop and I check my wrenches every year. Both wrenches are over 10 years old and neither one has requied any adjusting. As long as the wrenches are stored with the springs unloaded you should never have any problems.
* I also do not loan my torque wrenches out to friends. Using them as breaker bars ect are the #1 thing that will skew your readings.
