Im almost done building my northstar, and I want to check the cg. I check it when it's inverted, right? thanks

Yep.

>>Danger- engineering content<<<

The actual center of MASS is a little higher than the chord-line of the wing. if you balance upside-down, it will have more of a chance to pendulum and hang from the balance point. Right-side up, it's slightly more stable than balancing a vertical baseball bat on your fingertip. difficult up, easy down.

This is true of any low-wing plane.

If it STILL is hard to get a real reading, hang it by almost any point on the wing. a line straight down from your hang-point will cross the center of mass. Then hang it from a different point. A line straight down from THAT attach point will also pass through the center of mass. Where the lines cross is the center of mass.

Thanks for the warning Jim, I hadn't had coffee yet!