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Some protractors show the 360° revolution:

A 360 degree protractor.

When measuring a reflex angle, we measure the part of the angle that is more than 180° and add 180° to it. In the example the shaded part of the angle is 55°, so we add this to 180° to get the measurement for the angle, 55° + 180° = 235°.

Measuring a reflex angle
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