Precision is an assessment of the variability one may expect when the test method is used by one or more reasonably competent laboratories; the ASTM definition being "the closeness of agreement among test results obtained under prescribed conditions" . Estimates of within-laboratory variability or repeatability (sr) and between-laboratory precision or reproducibility (sR), represent standard deviations of replicate analyses. From the sr and sR, limits on the difference between two test results may be calculated, which are designated 95 % repeatability (r) and reproducibility (R). This is accomplished by multiplying the appropriate standard deviation by the factor 1.96*√2. Methods for estimating r and R and the standard deviations upon which they are based are given in ASTM E177 − 86 . The estimates from each clinker were pooled using the standard formula for pooling variances and standard deviations .