On the calibration of rotational instruments for the measurement of whole-blood viscosity

The Authors have looked at six proprietary rotational viscometers. It was not practicable to examine them all in the same detail, but the information suffices to show how results of reasonable accuracy may be obtained from any of them. Tests on Newtonian liquids show that these instruments have calibration-factors which are essentially functions of the shear-rate to which the calibrant is subjected. In some cases, the calibration factor is also strongly dependent upon the viscosity of the calibrant itself. However, it is shown that all of these instruments can yield results on Newtonian liquids with an accuracy of about ± 3%, but only at rates of shear involving sufficiently high torques. Having looked at the different responses of these individual instruments, the Authors recommend that users should calibrate their own instruments against a range of Newtonian liquids. The accuracies mentioned above are, of course, for Newtonian liquids; and when the viscometer is used in blood-studies, adoption of a wider error-band may be necessary.