What brand is it and where did you buy it? It appears to be used to level the cradle that the prop is mounted in. I take it there was no user manual included.
Hi Pixelzombie,Got it on ebay, and you are correct about the manual.
This is the way to go. I tried the glass method with my balancer and it spins more freely and seems less affected by the unbalance blue nuts.I have a drawer full of prop balancers including the DuBro. After testing them all, I went back to the water glass method which has given me reproducible results and the best accuracy.