Table 1.

Major measurement characteristics of Dualex 4 Scientific. Repeatability (instrumental variations) was evaluated by the standard deviation (sd) and percent standard deviation (%sd) for 30 consecutive measurements on a leaf with mean Chl value of 21 µg cm⁻² and mean Flav absorbance of 1.8. Reproducibility (inter-instrument agreement) was obtained from the measurements among five different Dx4 on 80 leaves of four different species. Accuracy for Chl was estimated from the calibration against Chl extracts: root mean square error (RMSE) from Fig. 3 (N = 195) and percent RMSE (%RMSE) for a mean Chl value of 32 µg cm⁻². Accuracy for the Flav index was estimated from the comparison to Dualex 3 in absorbance units: RMSE from Fig. 2 (N = 74) and %RMSE for a mean Flav absorbance equal to 1.2

	Chlorophyll		Epidermal Flavonoids		NBI
Source of variation	sd	%sd	sd	%sd	sd	%sd
Repeatability
Clip closed	0.034	0.16	0.004	0.22	0.037	0.31
Clip opened between	0.132	0.62	0.004	0.22	0.063	0.53
	RMSE	%RMSE	RMSE	%RMSE
Reproducibility	0.713	2.4	0.034	3.4
Accuracy	5.03	16	0.185	15