For balancing translation. The installed RCS will be set to translate your vessel to the current direction, with the green arrow being the actual resulting motion. When balancing translation you want translation motion without any rotation, so you want to place your RCS around your CoM in a way that reduces the torque vector (red arrow) as much as possible.

For balancing attitude. Only with RCS, reaction wheels and engine’s gimbals not accounted. For balancing attitude you want to reduce the translation vector (green arrow) while keeping the torque vector aligned with the red marker. In most vessels you won’t need to do this since balanced translation implies balanced rotation, but this is not always true.

For balancing engine’s thrust. The engines used in the calculation are always the engines in the bottommost stage, if you want to disable some engines you can move them to a higher stage. This mode also allows changing the direction of gimbals, showing their produced torque.

For balancing parachutes. This mode activates the center of drag (CoD) marker and should help in positioning parachutes so that your vessel will touchdown with the desired attitude and velocity.

The forces displayed are of 3 types:

Part forces

Forces exerted by parts, they are colored cyan for RCS and yellow for engines.

Translation force or thrust

Colored in green, represents the translation motion of your vessel, essentially your vessel’s thrust. A small green triangle near the tip of the arrow indicates where it should be pointing ideally.

Torque force

Colored in red, represents the resulting torque the thrusters are exerting into your vessel. The effect of this torque is represented by a circular arrow, which is proportional to the expected angular acceleration. When you see a red arrow, it means that in the current configuration and with the given input your vessel will try to rotate, however, depending of your vessel’s mass and of its distribution this rotation might not be noticeable, you can gauge this with the circular arrow. Like in the translation force, a small red triangle would be indicating the ideal direction.

CoM

The Center of Mass marker, colored yellow. You should be familiar with this one.

DCoM

The Dry Center of Mass marker, colored red, indicates the center of mass for your vessel without resources. Which resources to remove when the vessel is "dry" can be configured from the Resources settings.

ACoM

This is the Average Center of Mass marker, colored orange, shows the middle point between the CoM and DCoM.

All forces are referenced to one of these markers, you select which one from the GUI. Checking how forces change depending of where your CoM is will help you to understand how to balance best your vessel, eg, for a vessel that docks with almost no fuel it would be best to balance RCS around the DCoM and ignore the CoM marker. If you want your vessel to be balanced in most situations you need to build your vessel in a way that keeps both center of masses as close as possible, or if you can’t achieve this, balancing around the ACoM marker would be the best compromise.

CoD

The Center of Drag, only enabled while in parachute mode. Shows the resultant drag force.

Shows some information regarding the current mode in use, usually the thrust and torque magnitudes, and buttons for change the current direction and center of mass (CoM, DCoM or ACoM).

Torque

Torque magnitude.

Thrust

Thrust magnitude. In engine mode, there’s a toggle for select between thrust at vacuum or at sea level of the selected planet.

Reference

Active center of mass of the vessel, click for change.

Direction (Translation mode)

Current movement direction, click for change or use the shortcuts.

Rotation (Attitude and Engine modes)

Similar to direction, but for attitude changes. In Engine mode there will be an "R" button for reset gimbals position.

Delta V (Translation mode only)

Available dV from RCS at current direction.

Burn time (Translation mode only)

Time RCS will last until running out of fuel at current direction.

Body (Engine mode only)

Selected body for TWR calculations, click for change.

TWR (Engine mode only)

Thrust to weigth ratio at sea level of the selected celestial body.

Vt (Parachute mode only)

Terminal velocity of the vessel for the selected planet and altitude.

Shows some information regarding the mass of the vessel.

Wet Mass

Total mass of the fully fueled vessel.

Dry Mass/Fuel Mass

Mass of the vessel without fuel / Mass of the fuel, click in label to toggle.

Shows a list of resources currently in your vessel, displaying the total mass or the total amount of each (click in the "Mass" label for change the reading).

You can select which resources should be used for calculating the DCoM position and the vessel’s dry mass, disabled resources will be removed and enabled ones will remain. For example, if you want to know your vessel’s mass and DCoM position when only the MonoPropellant is completely consumed, only disable the MonoPropellant.

Options for show, hide or change the size of the CoM markers.

You can open the settings menu from the small s button in the title bar of RCSBuildAid window.

Use application launcher

Disable/Enable RCSBuildAid’s button in the application launcher.

Use blizzy’s toolbar

Disable/Enable RCSBuildAid’s button in blizzy’s toolbar.

Show in Action Groups

Don’t hide RCSBuildAid when switching to the action groups screen in the editor.

Marker autoscaling

The CoM markers will change size depending of the camera distance (if you get the camera closer to your vessel the markers will shrink).

Shortcut

Enable RCSBuildAid with a keyboard shortcut, disabled by default. You might assign any key but no key combinations. Using ESC disables it.

export KSPDIR=/home/user/KSP
make

Libraries\
  Managed -> ${KSP_DIR}/KSP_Data/Managed
  Toolbar.dll -> ${KSP_DIR}/GameData/000_Toolbar/Toolbar.dll