Why can't I get my Hardy Instrument to zero?

I send a zero command to my Hardy Instrument and intermittently it will not zero. I can re-calibrate the unit and it will allow a zero command again for a while, then stop again. What can cause this?

For the zero command to be successful your Hardy Instrument cannot be in motion and the gross weight must be within the zero tolerance of the calibration zero point.

You can check the motion status of your Hardy Instrument prior to sending the zero command.

When your Hardy Instrument is not in motion at the time the zero command is issued, and your current gross weight plus any gross weight previously zeroed off is within the zero tolerance parameter setting, then the unit will zero the current gross weight.

If your Hardy Instrument is not in motion when the zero command is issued, and it does not zero the gross weight, then normally it means the accumulated total of the current gross weight and previously zeroed gross weight exceeds the zero tolerance.

If the zero command starts failing, it would indicate the weight on the scale is changing and has changed enough to be out of tolerance for the zero to work. If, after a new calibration, it again will zero for a while and then starts failing, either the weight has changed enough on the scale to be out of tolerance or you have a bad load sensor that is causing the readings to change.

Typical setting of the zero tolerance is 2% of the maximum load. 

If you are sending the zero command over communications or through mapping (not using the ZERO button the on the front display) then auto zero tolerance is the parameter used to judge if the zero tolerance accumulation has been exceeded.