This reading tool has a graduated scale at the tip that lets you measure wafer heights directly in the keyway. Insert it like a key, note which wafers are high or low using the scale markings, and translate those readings into the correct key code. No impressioning damage to worry about.
Particularly useful on automotive door locks, motorcycle ignitions, and file cabinet locks where the wafers are too thin or the plug is plastic (making impressioning impractical). Comes with detailed instructions explaining the reading technique for different wafer configurations.