By adding and removing weights, we move from zero to the maximum of the scale in small steps, noting the weight and the corresponding readout of the scale. The more points we sample, the better will be our picture for the accuracy of the set-up. It might also be interesting to perform a calibration at different temperatures, because the scale might be not compensated perfectly with respect to the temperature influence. For each data point taken, we calculate the torque Q and prepare a graph showing torque versus readout of our scale. Ideally, the points on the graph should fall onto a straight line, which connects them all.
Any scatter indicates the accuracy of our equipment.
Friction should also be visible if the points from increasing the load follow a different curve than the points from the decreasing part of the data. Any friction problem might be reduced due to the vibrations of the engine, but it is no good idea, to rely on this hope. If the scale is non-linear, this is no problem, because we will use the calibration chart to translate the readout of the scale into torque. Therefore the graph should be done accurately and be large enough. For the measurements we need a sufficiently large stock of different propellers, which will cover the desired velocity of rotation range.