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Table 2 PLS calibration and validation parameters for regression models for date, pH, DP and zero-span tensile strength index (TSI); N—number of samples

From: Characterisation of 19th and 20th century Chinese paper

PLS model		Calibration					Validation
PLS model		N	RMSECV	Factors	R ²	Pre-processing	N	RMSEP	R ²
Five sheets	Date	112	21	6	0.6	SNV, MSC	33	24	0.53
	Date post-1900	86	9	9	0.67	SNV, MSC	29	15	0.47
	pH	135	0.5	8	0.66	MSC, S-Golay*, SNV	38	0.7	0.37
	DP	63	370	8	0.84	SNV, MSC, S-Golay**	21	690	0.52
	TSI	45	28	8	0.69	MSC, SNV, S-Golay*	–	–	–
One sheet	Date	112	21	7	0.64	MSC, S-Golay*, SNV	33	31	0.3
	Date post-1900	86	10	8	0.74	SNV, MSC, S-Golay*	29	13	0.41
	pH	135	0.5	7	0.63	MSC, S-Golay*, SNV	38	0.7	0.4
	DP	63	500	7	0.72	SNV, MSC, S-Golay*	21	720	0.55
	TSI	45	30	8	0.63	MSC, SNV, S-Golay*	–	–	–

Due to the low number of observations, independent validation was not carried out for TSI
*First derivative, three-point smoothing, second order polynomial
**Second derivative, three-point smoothing, second order polynomial

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