I've never heard of a proper way to measure bodyparts until I came across this:
Is there a general consensus on this? Is the wrist and hip approach correct?
Its purpose is muscle size goals. I would not benefit because I've already surpassed their goal measurements, except for waist that is. Ongoing battle. The answer is no, this is not an accurate measuring tool. I don't believe this is a measure for your potential.
No,there actually are standardized methods that exercise scientists use to measure.
Look up anthopometry on the internet, you should be able to find something.