When measuring angles using a protractor, how do you decide whether to use the top scale or the botton scale?
Usually, the bottom scale starts with zero on the right edge and increases to the left ending with 180 degrees on the leftmost edge. The top scale, on the other hand, starts with zero on the left edge and increase to the right ending with 180 degrees on the rightmost ...
This solution contains a very clear explanation of how to use a protractor correctly to measure angles. Specifically, it provides a step-by-step explanation of how and when to use the top scale and the bottom scale.