The MAC is the Mean Aerodynamic Chord. The application takes those simple measurements I listed above and tells you all that magic stuff. Truth of the matter is, all you're really interested in is where it says the NP is and where the CG is.

OH YEAH, you tell it one other thing. You also tell it a SM (static margin) to figure out for you. THEN you click the button right below. I think everything you have to tell the application is in the box at the very top of the page. And the "tell me" button is in that box too. When you click the button, all the other informational boxes instantly pop all the magic numbers. You only need one, the CG. They give you how far back on the wing root it'll be. Just like everybody does, even the ARF manual does. Only this one will be dependable as heck. You might note the Neutral Point as well.

I've used the sucker on just about every ARF I've built since getting back into the hobby a year or so ago. Think that's about 18-20 of them. It's amazing to see what the application says and what some of the ARF manuals said. Actually, is rather disappointing.

I've found that it's worthwhile to get the CG location for 20% SM, for 15% SM, and for 10% SM. That only takes 3 clicks of the "tell me" button. Ok, you gotta enter 20% and click, 15% and click, 10% and click.

Write all of them down. I usually write 'em into the ARF manual right over the manual writer's suggestion.

I've found that the geistware 15% SM works like gangbusters for me for maiden flights. The 20% geistware CG location is good for most 1st year flyers. I don't start a new airplane off at 10% only because the elevator is going to be so effective it's sometimes hard to sort the trim. However, I've got a number of models that now have their CGs at the 10% or so location. But they got their neutral elevator sorted at 15% and their elevator throws roughed out at that same 15%. THEN it was entirely safe to move the CG back, and the geistware had clued me in as to how far to go. When I do that step nowadays, it's a slam dunk to move the suggested amount, AND I also move the elevator connecting rod out one hole on the elevator horn. I go ahead and move the elevator connection to reduce the throws because the elevator effectiveness (NOT the airplane's stability) is going to change with the CG move. I've already tuned the elevator connection at 15% for good safe deflections, and know that much won't be needed nor desired with the aft movement of the CG. It's worked every time.