That. If you have the tools and the Gary Willis setup guide (which relies on feel and "about a credit card height" instead of "0.000102312342341230123100 inches" for measurements), you can do a setup.
Having spent many years in work where close tolerances were required, I'd bet you could show 10 random people a line the thickness of 2 (or even 3) cards stacked and they would say, yes, that looks about the thickness of a credit card.
Point being, there is a whole lotta latitude in setting up a bass that will function, but like anything else, good enough is not always ideal.
I've only been doing setups for a (relatively) short period of time but every bass player who has picked up any bass I've set up for myself wants to know who did it for me, they assume it's a professional set up. I pick up basses set up by their owners and they are all over the map. While this is not a big surprise as set up is an individual preference, strings not matching the FB radius or one sitting significantly lower than the other 3 is something one can't help but notice and wonder why it was set up in such a manner.
I understand the reason a set up method using dimensions on the order of "about the thickness of a credit card" are so popular. It's because most people touting their ability to set up their bass don't know what the proper drag on a feeler gauge feels like, they get confused by numbers expressed in decimals, and like most, can't read a scale graduated in sixty fourths of an inch.
The "about the thickness of a credit card" method is also proof simple that kinda sorta close enough is good enough for most people, but give those same people a bass set up by someone actually capable of doing it to "0.000102312342341230123100 inches" and their first thought is "professional setup".
One of the most common complaints in set up & repair is fret buzz, and the common answer is fret job by a pro. I'd bet a dozen doughnuts to a pint of stale urine a majority of those buzz complaints could be corrected with a better set up than the owner is capable of.
