Side note: I always bold the "is" in the legend line. This is not required, but I like to do it because it makes it clearer at a glance which part is the shorthand and which part is the full attribute text.
APR is the annual percentage rate
I use this functionality occasionally. Usually it's when I've got calculations in Word tables and I'm trying to make the left hand column more readable, e.g. using something "APR" in the formula so that it doesn't take up so much space.
[legend]APR is the annual percentage rate the result = APR * 10