Measuring for custom pushrods

Right, I guess I need to word this a bit differently. When I put my pushrod length checker in, am I doing the process with the marker correctly? Also, I got word that the lkfter needs to be on the bottom side of the lobe and I make the pushrod larger until there is no play, them make it .020" longer.

Now I understand what you said, but knowing how to dial in the correct length is where im lost. Do I adjust the length and just determine the length as to how much the valve opens, or by how the rocker arm rides on the valve tip?