Treat squareness as an absolute. You will fail anyway but in trying
for the absolute you will come as close as possible - by definition.

Treat the difference between the diagonals as an absolute. You will
fail anyway but in trying for the absolute you will come as close as
possible - by definition.

Remember the following:

Measuring Stuff Is Impossible

A recent thread on using tape measures in the shop got me to thinking
about this.

I went on Starrett's website and found that the most that they will
write up a Certificate of Accuracy for on a tape is +/- 1/32". They
also say on that website that whatever tool you use to measure with
should be capable of measuring to 1/10 of what your tolerance is. So,
if their best tape is only capable of +/- 1/32", then my tolerances
can't be any tighter than 5/16", which seems a tad generous to me for
cabinet work.

I have some Starrett and Rabone-Chesterman metal rules that will
measure to 1/64", which would allow me to have tolerances of a little
heavier than 1/8". I guess I could use these rules for framing houses
- but they still aren't accurate enough for building cabinets.

I have a Starrett dial caliper that will measure to 1/1000" - now that
will let me have tolerances of about 1/100", which is heading in the
right direction but when I think about it, a piece of newsprint is
about 4/1000", or 1/250" and I know that my joints are tight enough,
when they are cut properly, that I can't fit a piece of newspaper into
them.

And yet, that can't be possible because the best measuring instrument
that I have in my shop will only allow me to have tolerances of
1/100".

It makes you wonder why framing carpenters and masons even bother to
own measuring devices at all and, it has been my suspicion for some
time that many of them don't.

It is gratifying to me that I am capable of doing the impossible but
it makes me a bit squeamish, if you follow me. A man needs to know
where he stands in this world and how can you do that if you can't
measure anything proper like?

When I had my first philosophy course in college we studied this old
boy named Zeno the Eleatic and his paradoxes. Now, Zeno said that you
can never get from one place to another because, first you have to
cover half the distance from A to B, then you have to cover half of
the remaining distance and then half of that remaining distance, and
so on for ever and ever. So, there's no sense in trying to measure
anything because it just ain't gonna work out.

Zeno may have been the first framing carpenter, although I am not
entirely sure about that - nor anything else, it seems.





Regards,

Tom Watson
http://home.comcast.net/~tjwatson1/