RPM's gauge has a graduated scale along the upper edge of the base with easy to read lines and numbers. Each graduation on the inch scale (81300) represents 0.025" and on the metric scale (81150), 0.5mm. (for extreme accuracy, the graduations are far enough apart that they may be split to read as little as 0.012"  or 0.25mm. )! Included with the gauge is a spring-loaded tensioning knob to keep the gauge positioned while checking & setting positions on the gauge. The RPM 81300 Ride Height Gauge (inch scale) has a range from 0.150" to 1.150" (5/32" to 1-5/32") and the 81150 Ride Height Gauge (metric scale) has a range from 4mm. to 29.5mm.! RPM's ingenious design uses a base and a slide that travels along a twenty degree angle. By using such a slight angle, the accuracy of the gauge increases dramatically while still allowing a broad height range. Either gauge may be used to check most on-road or off-road vehicle's ride height, including pan cars & sedans! It's extremely easy to use and is the most accurate tool available on the R/C market!