Measurement of wall friction is similar to measurement of shearstresses, the only difference is that the powder shares on a wall sample.
For measuring of the static friction we need several repeading steps of shearing until the static friction gets to maximum. The dynamic friction value follows the static peak. Usualy the friction is measured starting with the lowest pressure and increasing the pressure for furter steps.
It is important to simulate the roughness of the surface of the plate. Differences can be many hundreds of percent. A wrong choice of roughness can lead big mistakes, such as collapse of silos.
The test palte for the measurement can be round or hexagonal.