Let InDesign Do the Math for You!
We've set one unit of measurement for the document or application, but as we've seen above InDesign will accept values in several measurement systems, as long as you specify which one: p12, 2cm, 30mm, and so forth.
Not only will InDesign think in whatever measurements you tell it to, it will also perform calculations in any dialog or palette that will accept numbers. You can use addition (+), subtraction (-), multiplication (x), division (/), or even percent (%).
Let's say in this example that we want the body copy to be one-and-a-half times as large as it currently is. We can grab our calculator and do the math ourselves, or, we can append "* 1.5" to the current point size of the type.
You can even change which measurement system InDesign thinks in, several times in one calculation if you wish! Need to know 0.1 inches + 2 centimeters? No problem, just type them in, no need to look up conversions. In the above example, I've changed the paragraph's space after attribute to .1in+2cm, which InDesign then converted into the document's default measurement system: 0.8874 inches.