I found this site that I occasionally glance at when I am feeling
particuarly pedantic.

http://www.wsu.edu/~brians/errors/errors.html




"WillR" wrote in message
...
Michael Lehmann wrote:
this is what they told us at university
Accurate means "capable of providing a correct reading or measurement."
In
physical science it means 'correct'. A measurement is accurate if it
correctly reflects the size of the thing being measured.
Precise means "exact, as in performance, execution, or amount. "In
physical
science it means "repeatable, reliable, getting the same measurement
each
time."



Actually that definition would not be very useful for eng., scientists,
stats. types and other mentally challenged workers.

Typically there you need to talk about "degrees of accuracy" -- hence
the need for agreed upon precision.

But this is boring stuff -- and I only care about the +- for the
micrometer on the lathe these days. (Just kidding)

The definitions are very important if you work with compound angles and
are designing multi component systems - particularly with spindles being
linked at compound angles -- as recent experience has reminded me. If
you forget to account for error factors the parts won't mesh -- or they
shove each other to the wrong place and something further down the line
doesn't work. You need to _know_ how much slop to design into a
system... Even then you normally have to _tune_ the fit at the end of
the process where the errors became excessive in the limit points..

(It's an issue in the above because you must work with Tangents
(rise/run) sines, cosines and so on and multiple calculations -- not
allowing for error gives pretty ugly results)

...Then the theoretical knowledge is like manna from heaven -- wonderful
to have at the right moment...

Arch was just tweaking my nose -- but as usual he raised a useful topic.

It really is important if you design -- less so if you work with plans
-- or just fiddle.

--
Will
Occasional Techno-geek