**5.4. Best calibration method**

Principal component analysis and regression lead to acceptable results but the best calibrations were obtained with ANN and PLSR. However the computation effort is much higher with ANN and in general more samples are necessary for a successful training. PLSR is a linear operation and can be performed fast in real time. For this reason PLSR is the best choice for calibration of the application discussed here. In Table 2 the results of both test series are compared with similar experiments presented in several other publications. As can be seen, the performance obtained here is in the upper range. However one has to take into account the further advantages of the system discussed here: it is non-contacting, the objects can be rotated, and can have irregular shapes and sizes.


**Table 2.** Comparison to other publications regarding the accuracy of the determination of moisture or water content. Except the method investigated in ISOPerm, all others are contacting and/or require a defined shape of the object under test.
