Table 5.

Performance comparison of factory (displayed in Table 3) and our own calibrations for direct regression approach of ThetaProbe: R² values, averaged AD (vol %), and RMSE values (vol %).

Calibration Type	Tested Material	Packing	R2	Average AD (vol %)	RMSE (vol %)
Linear own	Soil	Moderate	0.953	1.78	1.46
Polynomial own	Soil	Moderate	0.999	0.19	0.16
Linear own	Sand	Loose	0.982	0.92	1.08
Polynomial own	Sand	Loose	0.997	0.35	0.47
Linear own	Sand	Moderate	0.998	0.34	0.41
Polynomial own	Sand	Moderate	0.999	0.22	0.24
Linear own	Sand	Compact	0.990	0.79	1.10
Polynomial own	Sand	Compact	0.997	0.59	0.62