We will agree to disagree on the "is junk" part.
And I believe I did think about it. I came to the "accurate measurements
party" pretty late and therefore everything I have is digital. A mechanical
vernier caliper may not have any way to set the zero datum but all of my
digital ones do. So I have naively set the zero as needed and gone about the
business of getting what appear to be accurate measurements - i.e. things fit
together when I am done - without any problems.
Arvid
----- Original Message -----
From: David Scheidt
To: Arvid Jedlicka
Cc: shop-talk
Sent: Sunday, November 01, 2009 11:33 AM
Subject: Re: [Shop-talk] Micrometers
On Sun, Nov 1, 2009 at 7:56 AM, Arvid Jedlicka <arvidj@visi.com> wrote:
Looking at your diagram, I disagee that 'A' must equal 'B'.
Assuming you can 'zero' the caliper when the two 'B' jaws are together
then the measurements should be as accurate as when you 'zero' the caliper
when the two 'A' jaws are together and take a measurement.
Note that this is different than saying "when the 'B' jaws are together
then the 'A' jaws must also be together", which is what I think you are
after.
Any caliper where this isn't true is junk. It's true even on my insanely
cheap plastic calipers that I keep in the pen jar on my desk. Same for the
depth probe. Think about it. Vernier calipers have no way to zero them. All
three measurements are read from the same scale. So if one says zero, they
all should be at zero. anything else is an inaccurate measure.
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