"Jeff Wisnia" wrote in message
...
Robert Swinney wrote:

Not sure what Dan means here. If they were all. say, 89.5 deg. and
you nested them all together, they would be in agreement - but they
would not be 90 deg.


You place them "back to back" on a (good) surface plate. If there were
only two, and they were both off the same amount in opposite
directions, say at 89 and 91 degrees, they'd mate ok and you wouldn't
know, but if there's 3 or more and they "black out" in all
permutations, then they all must be damn close to 90 degrees.

Same principle as scraping and checking three surface plates against
each other.

snipped

Jeff





--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

There is no need to compare squares.

The simple method is to draw a line across a smooth clean piece of
stock, metal or timber, then turn the square over and draw another line
across the stock on top of the first.
If the square is any good the lines will be as one but any error will
show them diverging at twice the error.
--
John G

Wot's Your Real Problem?
..