Other than the below this is a good how to.
The guy contradicts himself in his own video, if .23 fit in the gap you would NOT put a smaller shim in it will just make the gap bigger. He measured it correctly the first time at .36 as you do not want to measure the entire face of the shim as it will bind slightly raising your indicated thickness. He then puts in a bigger shim from .36 to .37 and the larger shim reduced the gap to lower than .20.