Two problems have arisen with the Polished Stone Value (PSV) determination as specified in BS 812: Part 3: 1975: (a) The small pneumatic tyre is no longer being manufactured. (b) The control stone is no longer available following closure of Enderby quarry. This report describes the modifications that have been made to the procedure that allows the use of alternatives to the pneumatic tyre and control stone. It also gives an account of a programme of co-operative testing, discusses the results and gives estimates of the precision of the test. The conclusions were:- 1. The modified test procedure gives PSV results that do not differ significantly from those given by the BS 812: Part 3* 1975 test. 2. The repeatability and reproducibility of the modified test procedure are independent of PSV level and are estimated to be 4.3 and 6.0 units respectively; these compare with estimates of 4.9 and 6.0 respectively for the 1975 test procedure. 3. An alternative to the control stone gave results that were identical to the new control and therefore could replace it should the need arise. (A)

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