There is nothing magic about checking pushrod length. It is something you need to learn to do if you are going to build your own motors. To do this, I take a magic marker and blacken the end of the valve where the rocker arm rides. I adjust the valve and then rotate the motor until the valve goes through a complete cycle. I then remove the rocker arm and look to see how much of the marker has been wiped off and what part of the valve end is clean. When you have the correct pushrod length installed, this wiped area should be in the center of the valve. If it is not, repeat the process using the push rod checker until the pattern is back in the center, then measure the length of the checker and order that length push rod. If you do not have a mic big enough to accurately measure it, you can get close enough by standing the tool and a stock length rod perfectly straight on a level surface and use a feeler gage to measure the difference between the two and add or subtract . Or you can take the checker to your local machine shop and let them measure it for you. When I built my 383, I used Edelbrock Etech 200 heads and Competition Cams Pro Magnum roller rockers. I had to get new pushrods that were .25" shorter than stock (Yes, 1/4 inch!) Had I not checked there was a potential of destroying the valve train since the pattern center was on the edge of the valve stem!