Disclosure: I work with CraneScale UK (cranescale.co.uk), a UK supplier of digital crane scales.

A crane scale does not see weight the way a person does. It measures force, then turns that force into a number you can read from the floor. The part that does the sensing is a load cell: a small metal element that bends a tiny amount when the hook is loaded.

Most industrial load cells are strain-gauge devices. Thin foil gauges are bonded to the metal. When the metal stretches, the foil stretches with it, and its electrical resistance changes by a very small amount. That change is proportional to the force, within the cell's working range. The scale does not measure kilograms directly. It measures a resistance change, then maps that change onto a weight reading.

The signal is tiny, so the indicator amplifies it and converts it from analogue to digital. Filtering smooths vibration from a swinging load or a hoist motor.…