What is the difference between high and low calibration?

Traditional hard calibration methods, using test weights, require two points of reference for a calibration.  A "low" point and a "high" point weight change. The low calibration point is normally an empty scale for a zero weight reference point. The high calibration point is a known amount of weight on the scale equal to the "Span" value.  This develops the internal counts or increments per weigh unit.

The usual hard (traditional) calibration procedure would be to empty the scale, perform the low calibration, then place the span weight on the scale and perform the high calibration.

Hardy Process Solutions offers another calibration method. C2® calibration on most instruments.  This method allows calibration without the need for test weights.  The internal counts or increments per weigh unit are calculated and only the "low" point or reference zero needs to be established.