Starrett C19 Chrome Protractor Double graduations from 0-180 degree in opposite directions permitting the direct reading of angles and supplementary angles The back of the tool is flat for ease of use The blade can be locked firmly at any angle by the lock nut Satin chrome finish for ease of reading and resistance to rust Double graduations from 0 - 180 degrees in opposite directions permitting the direct reading of angles and supplementary angles The back of the tool is flat for ease of use The blade can be locked firmly at any angle by the lock nut Satin chrome finish for ease of reading and resistance to rust