(1) A bow spring or lever on a downhole [[tool]] which presses against the [[borehole]] wall to centralize the tool, to push the tool to the opposite side of the borehole, or to hold a sensor [[pad]] to the borehole wall.

(2) To prepare a perforating [[gun]] so that it will fire when the firing switch at the surface is operated. This usually requires connecting the [[detonator]] and/or completing the electrical wiring in the gun.