A4.3 Calculate the standard error of the accepted reference
value (SEARV) by dividing the CEU by the coverage factor, k,
listed on the supplier’s label or included documentation.
SEARV 5 CEUARV
k (A4.1)
NOTE A4.3—Standard Error (SEARV) is equivalent to Combined Stan-
dard Uncertainty (UC). See NIST Technical Note 1297.
A4.3.1 If the coverage factor, k, is not known, use the value
2.
A4.4 Construct the acceptable tolerance zone:
TZ 5 61.44 =σsite
2 1SEARV
2 (A4.2)
A4.5 Worked out example for kinematic viscosity zone
(band):
σsite 5 0.19 % ~default value from A4.1.1! (A4.3)
CEUARV 5 0.22 % ~from the CVRS label or documentation!
k 5 2 ~from the CVRS label or documentation!
SEARV 5 0.22
2 5 0.11
TZ 5 61.44=0.192
10.112 5 61.44=0.036110.0121 5 60.32 %
A4.5.1 In this example, the tolerance zone will be 60.32 %
of the certified viscosity reference standard value on the report
of test or bottle label. If this site uses a CVRS (for example)
with a kinematic viscosity of 33.98 mm2
/s, the TZ =
33.87 mm2
/s to 34.09 mm2
/s, with 95 % certainty. Viscosity
measurements made with this CVRS at that site should fall
within that tolerance zone (band) 19 out of 20 times.