What tool would be least effective for checking wheel alignment?

The tire pressure gauge is least effective for checking wheel alignment because its primary function is to measure the air pressure within the tires, rather than the angles of the wheels relative to each other and the vehicle's geometry. Proper tire pressure is crucial for tire performance and wear, but it does not provide any information about how well-aligned the wheels are.

In contrast, the other tools focus specifically on measuring aspects of wheel alignment. A camber gauge assesses the camber angle, indicating whether the wheels tilt inward or outward at the top. A toe gauge helps measure the toe angle, which assesses the direction the wheels point relative to the centerline of the vehicle. An alignment rack is an advanced tool that provides a comprehensive assessment of all alignment angles, including camber, toe, and caster, and can accurately diagnose alignment issues. Thus, while maintaining proper tire pressure is important for overall vehicle performance, it does not contribute to assessing wheel alignment.