Here is how the pugmill operator at Plainsman Clays gauges the stiffness coming out of the pugmill. That roller is on a slant and weighted. The softer the clay the more lines show. When they are like this (5th line steady) they know the water content is around 22% for this clay, Polar Ice. For other clays it is different. Stiffness at pugging must compensate when the clay tends to stiffen or soften over time on storage. Over the years they have tried many devices to measure stiffness, but this has proven the most reliable.
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