It's really easy. Let's look at it as a whole.

Take 9 measurements and type them in. Type a value of 5 into the Static Margin box. Click the button just below the SM box. Look down the page and find the CG location in the Calculated Results box.

Now let's take that a step at a time.
1. I use a yardstick to measure with. Half span, root chord, tip chord, and leading edge sweep are done for both the wing and horizontal tail. That's eight. The ninth is from the LE of the wing to the LE of the tail. The picture of the airplane planform that's on the geistware page shows those 9 measurements if you have any doubt where to measure.
2. To get a CG range, you'd run the application twice, once witha 5 in the SM box, and once with a 15. You can use other numbers, but if you're looking for a safe, reliable range, those are good for anyone unfamiliar with the values.


The good thing about having a range is it shows you when you're trying to adjust your CG on the bench, just where you need to get to and how far the actual CG is away from being in a safe range of locations. It makes it quite a bit easier to deal with moving a CG since you're not trying to hit an exact point that isn't "exactly" important. Yes, of course it's important, but the exactness isn't. We've developed a lot of slightly right, slightly wrong beliefs about the CG and using a range to balance clearly shows a developing modeler a lot more about the process. You will discover that some planes have narrower ranges than others. When you fly them, you'll often get a lesson on why. Some will have a wider range etc etc.......... But you'll certainly be coming up with an easier to discover and more reliable range.