The veritas square level attaches to a steel square (steel rule, i-beam, etc.) with integral rare-earth magnets. Has a vertical slot with an integral clamp to hold a ruler 1" to 1-1/8" wide & up to 1/16" thick. May be used to measure rise & run of just about anything. May be used to lay out sloping cuts on drywall or to fit molding next to a stair stringer. made from extruded & machined aluminum; fittings are brass. Bubble level is accurate; bubble movement of 1/16" represents angular change of half a degree. Weighs less than 3 oz.