This is by far the quickest, easiest and most accurate way to measure valve spring installed height. You install our Height Mic just like you would a valve spring, then expand the tool until it has seated the valve, locks and retainer. This simulated seat pressure allows ultra precise readings. The tool is then read like a micrometer and is accurate to .001". The short model is for 4 and 6 cylinder engines, while the taller version covers most V8's.