Types of trigonometric scales

Trigonometric scales on slide rules are presented in different ways. The following table shows the main variants.

 Type Variant Notes Scales on stock Scales on slide Front face Reverse face - marks on back of stock Reverse face - slide has to be reversed Same as with scale on front face of slide. Differential trig scales Patented - only on Thornton rules.

The next table looks at the suitability of these main configurations for three different types of calculations:

• Multiplying the sin of an angle by a number. This occurs in a right angled triangle if you know the length of the hypotenuse and the angle and want to calculate the length of the opposite side. Example: 5 * sin (36.9°) = 3
• Dividing a number by the sine of an angle. This occurs in a right angled triangle if you know the length of the side opposite the angle and wish to know the length of the hypotenuse. Example 3 / sin (36.9°) = 5
• Multiplying a number by the sine of one angle and dividing it by the sine of another. This occurs if you know one length a and two angles A and B in the formula  a / Sin A = b / Sin B and you wish to calculate the length b. Example 3 * sin(30°) / sin (45°) = 2.12

The following assume use of the trig scales with the C and D scales. On some rules it may be necessary to modify the instructions slightly for use with A and B scales.