The Straight Protractor is a ruler designed to draw and measure angles with a ‘positioning disk’ in the middle, ‘centimetre’ measurements at the top, and the protractor on the underside.
Chi Ningjun, Zhao Lishan
Set in the middle, the protractor is a red ‘positioning disk’, around which the ruler can rotate to any angle. ‘Centimetre’ measurements are indicated at the top, and the protractor measurements are on the underside. Users press and hold the positioning disk while rotating the ruler to draw or measure the angles.
Specific operating steps (corresponding to images 1 to 4):
Step 1. Draw a line OA, place the underside of the ruler (marked with red) along the line, so that the desired axis point ‘O’ corresponds with the ‘30’ mark on the ruler.
Step 2. Press and hold the ‘positioning disk’, rotating the ruler until the top of the ruler (marked with black) corresponds with the axis point ‘O’;
Step 3. Starting from ‘O’, draw a line along the ruler as ‘O-B’;
Step 4. A 30-degree angle is completed.