## Precision Accuracy and Uncertainty

It is important to understand three characteristics of numbers in solving agricultural problems: precision, accuracy, and uncertainty. Precision refers to the size of the unit of measure used to obtain the number. For example, if a sack of feed is weighed on a scale measuring to the nearest 0.1 lb, the weight is not as precise as it would be if the smallest unit of measure was to the nearest 0.01 lb.

The accuracy of a number refers to the number of decimal places obtained in the answer. The greater the number of decimal places, the greater the accuracy. A measurement of 12.15 ft is more accurate than a measurement of 14.4 ft.

The uncertainty of a number is the amount it is expected to vary. If the uncertainty is not stated after the number, say, 14.5 ft ± 0.01, then you may assume it is ± half of the smallest unit, Table 2.1.

Table 2.1. Level of uncertainty.

 Number Uncertainty 25 i 0.5 15.7 i 0.05 2.567 i 0.0005

Source: Theory and Problems of Technical Mathematics, Schaum's Outline Series, McGraw-Hill Book Company, New York, 1979.

Source: Theory and Problems of Technical Mathematics, Schaum's Outline Series, McGraw-Hill Book Company, New York, 1979.