Paint viscosity testers are used to measure liquids quickly and easily in order to determine their viscosity. However, it must be taken into account that this is only possible with less viscous liquids. Viscous pastes and other substances with a high viscosity are not suitable for measurement with a flow cup. The structure of a flow cup is standardized according to a DIN and is therefore always the same. It consists of a cylindrical hollow body which in most cases ends in an exchangeable nozzle. The openings of the nozzles, like the cup, are subject to a respective DIN standard.

Measurement is carried out as follows. First you hold the nozzle underneath closed and fill in the substance to be measured. Make sure that the cup is filled to the top. An overflow channel prevents the measurement from being falsified by liquid running off the sides. Then the glass plate is pushed over the edge of the cup to remove any excess material. You can now open the nozzle again. The resulting negative pressure keeps the material in the cup. If you now pull the glass plate horizontally from the beaker, you have to activate the stopwatch. As soon as the outflowing stream breaks for the first time, you have to stop the time and note it down.

When using a flow cup, it is particularly important to ensure that it is cleaned thoroughly after each measurement, as residues in the nozzle and cup can falsify the further results. Even deep or many scratches in the cup can lead to measurement uncertainties in the result, since the removed material changes the volume of the cup and thus no longer complies with the specified DIN standard.