9.3 The multilaboratory standard deviations for slump, unit
weight, air content, and 7-day compressive strength of trial
batches have been found to be 1.0 in., 1.4 lb/ft3 0.4 %, and 347
psi, respectively; therefore, the results of properly conducted
tests on single trial batches made in two different laboratories
should not differ by more than 2.8 in., 4.0 lb/ft3, 1.1 %, and 981
psi, respectively. This precision statement is considered applicable
to laboratory trial batches proportioned to contain prescribed
quantities of materials and to have a prescribed
water-cement ratio. The values should be used with caution for
air-entrained concrete, concrete with slump less than 2 in. [50
mm] or over 6 in. [150 mm], or concrete made with other than
normal weight aggregate or aggregate larger than 1 in. [25 mm]
nominal maximum size