They typically measure some angle of refraction or the critical angle for total internal reflection.

Rather than attempt to measure the angle of the resulting cone directly, divide the height by half the width of the base of the cone.

This permits him to measure the angle between the horizon and the sun as the sum of the angle read from the two arcs.

The operator could then measure the angle to the target radio source by performing direction finding within this small area.

Both right ascension and longitude measure an angle from a primary direction (a zero point) on an equator.