A caster-camber gauge is an instrument that measures two of the three most important angles in the geometry of the front end of a road vehicle. These are the camber and the caster (the other important angle is called the toe). Using bubbles, the gauge indicates the degree of tilt and can therefore be used as an aid in aligning the front of the vehicle.

Camber is the tilting of the wheels from the vertical when viewed from the front of the vehicle. When the wheels tilt outward at the top, the camber is positive; when they tilt inward at the top, the camber is negative. The amount of tilt is measured in degrees from the vertical. Camber settings affect the directional control of the vehicle and tire wear.

Caster is the tilting of the uppermost point of the steering axis either forward or backward (when viewed from the side of the vehicle). A backward tilt is positive; a forward tilt is negative. Caster influences directional control of the steering but doesn't affect the tire wear.

Bubble gauges have now been superceded in professional alignment shops by lasers and computer equipment. However, bubble gauges provided fairly accurate alignment capability for home garages and racetracks.

When aligning the front end of a vehicle, the camber is adjusted first, then the caster. This sequence must be performed repeatedly because the camber and caster alignments affect each other. Finally, when both are within specs, the toe-in can be adjusted