This is an Arduino controller board that has been wired to a display and a moisture sensor probe (which is stuck into a piece of soft clay). The sensor outputs a voltage that varies with changes in the resistance encountered between the probes (according to the material being measured). In this case the controller is directly outputting the number being returned by the probe. A study is needed to compare outputs with actual measured water content, this data would enable changing the software to output the percentage-of-water directly. However this sensor is intended for soils, it is not giving repeatability and consistency for measuring the much higher water content found in pugged clay. So we need to find a better one.
In ceramics, clays exhibit plasticity in accordance with their recipe but also the water content. The stiffness considered correct varies for different types of forming methods.