Rail-Height Gauge: When its time to position the handrail at a uniform height above the tread nosings, my rail-height gauge is much easier to use and more accurate than a tape measure.
The gauge, which works like an oversized T-bevel, consists of a wood measuring stick (my original one uses a yardstick) fastened to a 36-inch-long strip of 1/2-inch-thick plywood about 1 1/2 inches wide. The plywood strip has a 1/4-inch slot ripped exactly down the middle so that accurate readings can be taken regardless of which way the yardstick is swiveled. The two pieces are joined together with a plastic star knob with a 1/4-inch-diameter stud, a couple of brass washers, and a T-nut sunk into a hardwood block.
The hole at the bottom of the yardstick should be drilled so that its bottom corner is flush with the bottom of the plywood strip when the gauge is open to approximately 35 degrees (the pitch of a 7-over-10 stair).