You realize we're talking about 4mm difference here.
I would personally guarantee that if every foccer was to show how they do their own chain measuring techniques the results would have a vast difference among every bike.
They'll either be too tight, too slack, misaligned, chain too dry, or not lubed correctly on every link, etc.
What i've noticed over the years is that if a chain is misaligned, too tight, or too slack then your hearing should suss it out first.
Too slack and the chain will slap about, too tight and it will just be noisy plus you'll feel it grinding through your left foot peg.
If the chain is misaligned then a knocking/rotational grinding will be felt and heard as well.
When adjusting the chain, once the wheel nut is properly tightened up a simple spin of the wheel (on the centre stand of course) can reveal all of these traits quite easily.
If all is well then the chain will purr when the wheel is spun forwards or backwards, to the point that you just know that it's right.
There is a large amount of common sense involved here, as well as what is advised in the manual.