You can make a very simple CG machine. Get a 1"x4" board. Drill two holes in it about 6" apart. Stick a wooden pencil in each hole. Now place the plane on erasers of the pencils in the location were the CG is supposed to be. Adjust as needed to get the CG back to where it's supposed to be.

No need to spend a lot of money, you can make this one with stuff you probably have on hand.

Ken