Like 8 said, they really aren't used that much and I tune my engines about the same way as he does. I use mine a lot when I'm testing different props on engines or just making sure I'm not going over the rated RPM range on a new engine. I always use one on a new engine just to be safe. I don't think I have use a tach on one of my own engines in over a year, I just know when they are right. I did use it on a new gasser a few weeks ago and discovered I was getting too close to the top of the RPM range and went to a bigger prop to get it where I wanted. They do come in handy.