Common Symbols
The letter 'R' as shown is used widely in drawings and is short for the word Radius. Radius is the distance from the centre point of a circle to the circumference of a circle. It is always placed in front of the number. For Example R50, means the circle has a radius of 50mm. For more information go the section on parts of a circle.

The symbol on the left represents the diameter. The diameter is double the radius and is the longest possible chord you can draw in a circle. Similar to the radius, the diameter symbol symbol is placed in front of the number. For example, Ø50 means that the diameter of a circle is 50mm. In order to draw that circle you will have to divide it in two to get the radius, so you can swing it with your compass.
