1. This rule is designed for industrial quality control, both to avoid poor quality products leaving a factory and to keep the costs of sampling at a scientifically acceptable minimum.
2. This rule is quite large - 19.5 cm (7.7 inches) diameter.
3. Although the instructions for rule gives a brief description of some the terms it uses it does require some understanding of statistics.
4. Both faces of the rule have a solid outer disc, a thinner rotating disc and a cursor with, in effect, multiple gauge points.
5. The rule has seven different sections and these are described in more detail below.
6. The rule has 48 scales - more than any other rule in my collection.

The seven sections of the rule

This section has a series of scales giving the Poisson Probability that an Allowable Number of Defects in the Sample will not be exceeded when the batch from which it is taken has a certain percentage of defectives.

Ensures that a product is kept within acceptable, specified limits.

Enables upper an Upper Warning Limit and an Upper Action Limit to be calculated.

The calculator gives plus and minus action and warning limits for the average size of the items in each sample.

The calculator gives Upper and Lower Warning and Action Limits from the Mean Sample Range.

From the standard deviation this section determines the proportion of the product which will fall outside any Allowable Deviations specified.