Protractor

Protractor comprising:

• (a) a flat base having a corner portion, a first straight edge extending from the corner portion, a second straight edge extending from the corner portion at a right angle to the first straight edge and a degree scale extending between said first and second edges along a circular arc generated from a point on the corner portion,
• (b) a measuring arm mounted on the base for rotation about said point and having straight edges for cooperating with either of said first and second straight edges to form an angle corresponding to an angle to be measured,
• (c) an indicator arm mounted on the measuring arm for rotation about said point and having an indicator mark spaced from said point so that the mark coincides with said degree scale, and
• (d) locking means for fixing the indicator arm in a plurality of predetermined positions on the measuring arm so that in each position, the angle indicated by the mark on the scale coincides with the angle formed between at least one of the said first and second straight edges and one of the straight edges of the measuring arm, and the range of angles measured by the protractor is different for each of said predetermined positions.