I've worked at many places where our tools were calibrated. We were told by one of the calibration companies to store our torque wrenches in the lower 20% of the range, and not to store them as low as they would go. For clarity, these were torque wrenches that started at 50 ft/lb on the scale, but you could turn them down below that indication. The cal. company told us that if we stored them under the lowest setting, it took some of the preload off of the mechanism inside and would cause the reading to be off after awhile. At the time, we were using Proto torque wrenches, and it cost my company just as much to get our used torque wrenches calibrated as it did to buy a brand new certified torque wrench. My boss decided that he'd rather have new ones than to pay for calibrating something that had been used almost daily for a year. So, each year, there'd be at least 8 used torque wrenches given to whomever wanted them since we replaced them with the new ones. I've followed that persons advice ever since and it seems to work out ok for the random cross checks that I've done over the years.