If your reversing the hinge of an interior door or haning it for the first time, chiseling out the jamb to accept the hinge can be tricky.

A butt marker can make the job easier--mark off the placement, hammer in the marker, and the device marks off clean edges so you can chisel out the center more cleanly.

Stanley makes them, but they may be hard to come by so call your hardware store before going. Also, make sure you get the right size to match your hinge--they come in 3", 3-1/2" and 4" heights.