1. Basic manual handling systems

The prototype is the oil level dipstick in an engine crankcase, with two lines: high and low.

Industrial gauges, sometimes of rudimentary manufacture, are scarcely more complicated. A rigid graduated ruler is immersed in the liquid up to a fixed stop, the bottom of the reservoir in the most basic case, and the geometric height of the liquid is read off a scale, in situ if possible, otherwise by removing the ruler and marking the wetted height.

For tall containers, an easier-to-handle variant consists of a weighted ribbon wound onto a drum and unfurled.

Rigid gauges are mainly used for liquids, but they can also be used to measure the level of powdery or granular products...