These slick chassis height gauges allow you to preset the desired height and slide the gauge under the car. Adjust height til the frame rail touches the end of the tape. 24" for perimeter frames. Measures height from 2" to 10" (higher if needed) Works 3 ways - with scale pads or without. Works in 3 Different Ways Car on the ground - measures chassis height directly, accurate to 1/16". Car on scale pads - measures from top of pads - ground level - to frame directly (no subracting needed here). Measures chassis height dynamically, as you work on the car. Magnet holds tape to frame. Indicator shows height as the car moves up and down. Use set of 4 to quickly see height at all 4 corners. You don't even need to bend over.