I am a cabinet installer and have been using a pair of the cabinet jacks shown in the drawing for years. They work better than an extra set of hands to hold upper cabinets in place before I screw them to the walls. The key is the hinge, of course, which allows me to make minute adjustments up and down by simply changing the angle of the upright. If I need to install upper cabinets before the base cabinets are in place, I simply screw a couple of extension legs to them.
Kenny Eident, Fort Mill, SC