The outside dimensions of round or square stock are measured with a caliper rule.
Drawing lines with a rule
A rule and pencil can be used to gage lines parallel to an edge. Hold the rule in one hand, with the thumbnail at the desired dimension and at the same time in contact with the edge of the board. The rule must be kept at right angles to or square with the edge. Hold a pencil point firmly against the end of the rule. Move the rule along, holding the thumbnail against the edge of the stock and the pencil against the end of the rule.
The edge of the rule may also be used for drawing straight lines provided the edge of the rule is true. The folding rule, zigzag rule, or the flexible steel tape should not be used for this purpose, since the accuracy of a line drawn with these tools cannot be dependable. To connect two points with a straight line, place the edge of the rule on the reference marks. These reference marks should be as far apart as possible.
Hold the rule with one hand at the center of the rule. The pencil should be held at a slight angle so that the top of the pencil will ride along the edge of the rule.
Reading a rule
The accuracy of layout work depends a great deal on the ability of the woodworker to read a rule correctly. Rules are divided into large sections, each of which measures one inch (in the English-system rules). Each of these sections is subdivided into smaller units which are fractions of the inch. When an inch is divided into 8 spaces, each space is 1/8"; when an inch is divided into 16 parts, each part equals 1/16”.