Table 1.

Physical characteristics of papers.

		Standards (TCVN)	Questioned documents				RSD (%)
			A1		A2	A3
1	Mass (g m−2)	1270 : 2008	59.5		61.1	60.1	≤1.44
2	Whiteness (ISO, %)	1865-1 : 2011	91.1		90.8	90.7	≤0.25
3	Opacity (%)	6729-2008	86.2		88.6	88.4	≤1.74
4	Bekk smoothness (second)	6727 : 2007	Side 1	59.3	62.0	56.5	≤4.67
			Side 2	27.5	28.8	27.0	≤3.72
5	Air permeability (ml min−1)	6891 : 2001	1385		1392	1356	≤1.57
6	Thickness (mm)	N/A	0.041		0.039	0.040	≤2.5