I'm not quite sure that this is the right answer, but maybe there is something alike between a scale to measure weight - which I prefer to call it a "weighing scale" or a "bathroom scale" - and a protractor scale.

Inside a bathroom scale, there is the circular "dial", if I was not mistaken, that displays the weight of somebody when he or she stands on it. That "dial" will spin and stop at the exact spot where the right weight is displayed. It is similar to a protractor scale, even though it doesn't weigh people, it measures angle and instead of the protractor that spins when we wanted to draw an angle, our hand moves from zero degrees to the desired angle.

So, I conclude here that the similarity between a scale to measure weight and a protractor scale is just the circular thing inside that shows a value at the circumference of the circle.

(P/S: If you notice that I have a poor English, I'm sorry because I'm 12 years old only. I think I've succeeded to write the best answer.)

Inside a bathroom scale, there is the circular "dial", if I was not mistaken, that displays the weight of somebody when he or she stands on it. That "dial" will spin and stop at the exact spot where the right weight is displayed. It is similar to a protractor scale, even though it doesn't weigh people, it measures angle and instead of the protractor that spins when we wanted to draw an angle, our hand moves from zero degrees to the desired angle.

So, I conclude here that the similarity between a scale to measure weight and a protractor scale is just the circular thing inside that shows a value at the circumference of the circle.

(P/S: If you notice that I have a poor English, I'm sorry because I'm 12 years old only. I think I've succeeded to write the best answer.)