Making the most out of our graphical telemetry computers.

Like with many complex instruments, there are multiple ways to solve certain problems and to measure the required inputs. Combining the various functions leads to a multitude of advanced uses.

### Computing Sine (and Cosine)

It is often necessary to find the sine or cosine of an angle when performing a calculation. Finding the rough figure for sine or cosine given an angle is easy using a sine quadrant.

Two half-circle arcs, one centered on the sine scale, one centered on the cosine scale, can be used in conjunction with the sine and cosine scales as a method of converting angles.

If you haven't done it yet, now is a good time to install a cursor on the string. (Latin for 'runner,' a cursor is the name given to the transparent slide engraved with a hairline that is used for marking a point on a slide rule and which we are using on our quadrant to store a value and move it to a different scale.)

#### What's the sine of 36°?

1. Overhand-knot a small piece of string to the measuring string before the first distance knot.
2. Pull the string taut over the angle.
3. Move the sliding knot on the string to rest directly on the sine arc.
4. Once the marker is in place, rotate the string to the left-hand scale and read the result from the mark underneath the knot (35/60 or 0.58).

Conversely, to find the angle represented by a given sine, the process works in reverse.

Computing with the sine arc in conjunction with the sexagesimal scale and a moving cursor on the string.

Computing cosine is done in a similar manner. Notice that as the string is rotated from 0° to 90° the sine varies from 0/60 (0) to 60/60 (1) with the cosine changing in reverse from 1 to 0, as expected.