How does CAD scale objects to a specified size?

Some drawings only provide one size, as shown in the following figure

Many beginners do not know how to start when they see such a drawing, and always wonder how to determine the radius of the small circle in the middle. If you have a sufficient understanding of the usage and parameters of the scale command, this drawing is very simple to draw.

Start with the inner circle, with a random radius. Simply draw a similar shape and use the Scale command to scale the entire shape to the indicated size.

When specifying a reference length or a new length, you can directly enter numerical values or obtain the length from the drawing by specifying two points.

Therefore, using reference options not only allows the drawing to be scaled to a specified size, but also to the same length as other drawings.