A random sample of 72 farm milk tanks was check-calibrated to determine whether official tolerances for estimates of milk weights were realistic. The overall calibration error for 859 calibration check values was + 3.12 1b. Sixty-nine percent of all values exceeded the official tolerances and this was reduced to 23% when the calibration check values for each tank were reduced by an amount equal to the mean calibration check error for the tank. Under these circumstances the official tolerances were approximately equal to one standard deviation of errors. When the tolerances were doubled (approximately two standard deviations), the percentage of the calibration check values which were excessive was reduced to 4.9%. It was concluded that the official tolerances were too small and should be doubled in size, giving a tolerance range of 6 to 16 1b. (0.5 to 0.18%) for a range of tank capacity from 1200 to 9000 1b.

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