I've noticed I'm having to check the zero my caliper after each case measurement (several per case) because the zero is off a bit more often than it used to be, maybe .0005" when it should read 0.0000. Normally, I check the zero about every few cases, but not feel I have to check zero for each measurement. For example, I think this is happening maybe 5-6 or more times measuring seating depth of 75 rounds. Consequently, I'm having to check zero with each measurement and re-zero fairly often. I've used the caliper regularly reloading for maybe 5 years. I'm not sure if it's worn out or if I can fix this problem somehow. Any thoughts?