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The establishment of the NPL viscosity scale using glass capillary viscometers is described and the values obtained for NPL viscometers on subsequent recalibrations over a period of some years are given. The results of comparisons with independent viscosity scales in other countries are also tabulated. From the results obtained on recalibration of the NPL viscometers and the comparisons made with other independent laboratories, it is concluded that the present scale is realized with an uncertainty of about 0.2% at low viscosities (5 cSt) rising to about 0.5% at high viscosities (5000 cSt).
J E Daborn (1975) studied this question.