You can choose a preset or custom drawing scale so that distances in a drawing are proportionate to real-world distances. For example, you can specify that 1 inch in the drawing corresponds to 1 meter in the physical world. A preset drawing scale lets you set a typical scale, such as 1:2 or 1:10.
a. Click Tools > Options, or press Ctrl+J.
b. In the Document list of categories, click Rulers.
c. Click Edit Scale. (The Edit Scale button is not available if the ruler's unit of measure is pixels.)
d. Choose Custom from Typical scales list box, and specify the settings you want.

Tip provided by Silvio Gomes, CorelDRAW Master, Artist and Graphic Designer.