Accuracy and Uncertainty of Calibration
The accuracy of our calibration data varies according to the units used and
the viscosity of the standard.
Viscosities expressed in poise
| Oil Numbers |
Nominal viscosity accuracy
(as quoted on the oils range page) |
| U 0100 – U 2600 |
± 5% |
| U 2800 – U 4000 |
± 3% |
Viscosities expressed in Stokes
| Oil Numbers |
Nominal viscosity accuracy
(as quoted on the oils range page) |
| U 0100 – U 2600 |
± 5% |
| U 2800 – U 4000 |
± 3% |
Expanded Uncertainty
The reported expanded uncertainty is based on a combined standard uncertainty
multiplied by a coverage factor of k=2, giving a level of confidence of approximately 95%.
| Kinematic Viscosity |
Dynamic Viscosity |
Density |
| < 10 Stokes 0.35% |
< 10 Poise 0.35% |
0.07% |
| ≥ 10 Stokes 0.65% |
≥ 10 Poise 0.65% |
Viscosities expressed in Krebs Units
The viscosities that we quote in Krebs units have been calculated using
the method described in ASTM D 562-81(1990). This involves the use of an
equation to convert viscosity (in poise) to the load (in grams) required to
cause a Stormer viscometer paddle to rotate at 200 rpm.
The standard includes a table which relates the viscometer load to Krebs units.
There is no data in the standard showing how accurate this relationship is and
consequently we are unable to quote a value for the accuracy of our standards
when the viscosity is expressed in Krebs units. It is for this reason that the
values given in Krebs units are outside the scope of our UKAS accreditation.
