Which tool is best for verifying that equipment fastened to a wall is parallel to the ground?

A level is the most appropriate tool for verifying that equipment fastened to a wall is parallel to the ground because it is specifically designed to determine horizontal alignment. Levels utilize a liquid-filled vial with a bubble that indicates whether a surface is level (horizontal) or plumb (vertical). When the bubble is centered between the marked lines, it confirms that the equipment is perfectly parallel to the ground.

While a square is useful for checking right angles and ensuring that edges are aligned properly, it does not provide information about horizontal alignment. Similarly, a ruler is primarily used for measuring lengths or distances and lacks the functionality to assess whether something is level. A laser, although it can be used for alignment purposes, typically serves more complex applications such as projecting lines or points rather than directly measuring levelness in the simple way that a level does.