On the Pro 700 as long as you know your row width or swath width the math isn't difficult.  For instance, my lines are all made with a 40' planter so when I pull into a field with my 120' sprayer I almost always have to remark the line 40' left or right.  If I'm at a random spot in the field I'll use "set to current" and then adjust that to the nearest number divisible by 2.5' (30 inches) because that is my row width.  I've yet to figure out how to make this work on the Pro 1200