measurement of skidding resistance. part v. the precision of scrim measurements

this report describes an estimation of the precision of sfc measurements made with scrims. it is based on data collected in 1978 and 1979, when samples of seven and eight scrims respectively were assembled at crowthorne and comparative tests made both on a test track and on a public highway. the main findings were:- (1) under good operating conditions the variation associated with a single machine and its operation yielded a coefficient of variationof sfc averaging 2.3 per cent. (2) under good operating conditions variation associated with different scrims and their operation yielded a coefficient of variation of sfc averaging 6.1 per cent. (3) tracking errors can lead to a substantial increase in variability.(a)