In addition to the Plane COG Balancer https://www.thingiverse.com/thing:3227802, it can be helpfull to have it balanced even without a plane on.
To acheive that, this device has a left tank that can be loaded, and is hooked on horizontal bars touching the ruler left side.
And to ease stability a platform is added with COG axe mark. Adding weight on this platform will help the whole stability
Version 2 is easier to print as it includes support for the right hook and reduces the bridge need in the left tank.