How does the "depth of focus" change as magnification increases?

When magnification increases, the depth of focus automatically decreases. 

The term "depth of focus" is commonly used interchangeably with the term "depth of field". The depth of focus refers to the image space while the depth of field is object space. The relationship between magnification and the depth of focus is inversely proportional which means as the the other one increases the other decreases.

Where is the excerpt? it’s not attached