I used to balance high-speed grinding wheels. These things had to be perfect.

If you're balancing a prop, it doesn't have to be nearly as critical, but the same rules apply.

First, don't think of the prop as a 2-sided stick, think of it as a disk.

The video above shows how once the blades are balanced, you will still need to balance the other areas of the "Disk"

Now, that said, if the baldes are balanced, that is plenty good enough for any prop under 15"