have one balancer that I made with plywood,two wood dowels and two pencil erasers,If the plane is heavy the erasers will ding the covering on open bays,the other is by great planes which has worked well on most 12 # or smaller planes. on larger planes I'll build a balancer or use my fingers. To me the marked c/g is a starting point only,I'll fly the plane and trim to my style of flying,thing to remember is changing c/g, the other trims are affected.