Releasing the tension on the torque wrench's spring maintains its
accuracy, but most torque wrenches aren't very accurate when new,
especially cheap imported ones. Standard practice as per AC43.13 (and
required by aircraft maintenance law, at least in Canada) is to have it
calibrated when new, and then every year or two depending on use. It
can cost more to calibrate the thing than it cost to buy it, which is
why they're so inaccurate when boxed at the factory.

Dan