There are some videos on YouTube, but what one is better than the other, IDK. If you have a set of gauges, there are 3 things to look for. #1,High pressure at rest, so engine off, and looking at a chart for that.
#2 high pressure, with the engine running, and then
#3, low pressure, with the engine running.
All of this has to go along with the outside air temp. Humidity is a factor, but outside air temp, is what is more important. Also 134A is slow to react. Get things close, take it for a drive, then check it again, when you return. Look at some videos also, that explain how the office tube works. That's what makes the pressure different, from low to high.