I don’t know about any mechanical device, mathematical rule, or
textbook “method” - but when want I a discrepancy detected, a failure
of alignment found, a lack of symmetry seized upon, an eccentricity
elevated to consciousness, anything out of level or plumb pointed out
with unerring accuracy, here’s how I do it.
Without saying a word, I just let my dear wife come within eyesight
of the object and her radar immediately homes in and focuses a gimlet
eye upon the offense to propriety and good taste. She loses no time
in bringing the matter to my attention and here’s the best part - I
am always grateful. Sometimes it takes a while before my good sense
gets the better of my wishful thinking, but I am always, always
grateful.
My workshop buddy and i were just talking about this area of life
and work. He opines that while we strive for the best result, there
is no getting at perfection. Them who get on their high horses, the
ones for whom nothing is ever good enough - well, some may have
higher standards than others and maybe even the higher skills to get
closer, but for everyone there is a “good enough” point. Or else,
when would anyone ever stop working?
There is no point in seeking a mathematical answer such as your
query implies when you wonder if 1 miilimeter is “good enough”. That
number would depend upon the scale of the work. Bigger work = bigger
tolerances in general, along with other practical considerations
like the distance from which an object will be viewed etc.
Listening to an inspired piece of quite funky ol’ country blues not
long ago, my fiddler friend said “Wow! You don’t have to be in tune
to be good!”
For me, personally, the greatest challenge has always been overcoming
my desire to get to the point when I can consider a piece “good
enough” and start strutting my creation about for the approval,
admiration, or cash I hope it will bring to me. I don’t want that
desire to play tricks upon my eyes or to distort my judgement. So I
am grateful to have a dear, trusted second set of eyes to help keep
me honest, along with all the measuring tools on my bench. That
second set of eyes needs to have some other good qualities attached
to it - honesty, gentleness, firmness, are just a few. And I, of
course, have to be able to abandon defensiveness and ego and just
learn to listen carefully. Being a first-born son, that last is a
damned hard skill to learn.
Good luck
Marty