I've just measured a number of my old LPs, acquired or produced in a number of
countries (UK, USA, Canada, South Africa, France, Germany, USSR). The
European, South African and British ones are all exactly 300 mm in diameter,
+/- about 0.2 mm, no more. The American and Canadian ones are all 302 mm in
diameter.
I also have a couple of very old '10 inch' 78s. These are EXACTLY 250 mm in
diameter, not even a shade of a mm either way.
I would say records are in the first instance metric products.
John F-L
----- Original Message -----
From: Jeremiah MacGregor
To: U.S. Metric Association
Sent: Sunday, April 05, 2009 3:52 PM
Subject: [USMA:44383] RE: Records
Stephen asserts the records are true to their name (ie a 12 inch named record
is really 305 mm in diameter). But since the rounded metric sizes are the true
and original sizes, then they are metric based and only were converted to
inches for US manufacturing at the time. It is obvious from the RIAA spec that
the original metric based dimensions were still intended but that the slight
differences within tolerances occurred as they wanted them to be described in
inches in vulgar fractions.
How does one accurately express a rounded millimeter value in a vulgar inch
fraction and stick to either 8-ths, 16-ths or 32-nds? For example, if you were
an engineer in the 1920s and had to convert a European metric spec for American
use, how would you do it and still retain the same original dimensions in the
converted value?
Jerry
------------------------------------------------------------------------------
From: John M. Steele <jmsteele9...@sbcglobal.net>
To: U.S. Metric Association <usma@colostate.edu>;
jeremiahmacgre...@rocketmail.com
Sent: Sunday, April 5, 2009 10:34:35 AM
Subject: Re: [USMA:44375] RE: Records
Your dimension of 302 mm is correct, more correct than the nominal 12".
However, Steve's assertion that it is inch based is also correct, as written
in the specification.
Since the International size is claimed to be 300 mm, and 302 mm
differs from it by a few multiples of the tolerance, as an engineer, I have to
say they were engineered to be different sizes, even if they are "close."
Assuming the International size has a similar tolerance, they will not overlap.
--- On Sun, 4/5/09, Jeremiah MacGregor
<jeremiahmacgre...@rocketmail.com> wrote:
From: Jeremiah MacGregor <jeremiahmacgre...@rocketmail.com>
Subject: [USMA:44375] RE: Records
To: "U.S. Metric Association" <usma@colostate.edu>
Date: Sunday, April 5, 2009, 9:59 AM
John,
Thanks for verifying what I have said. We now have proof that I am
correct and Stephen is wrong. But I highly doubt Stephen will change his
position and continue to spout error.
The RIAA spec is very interesting as it butts up against an
interesting problem in converting millimeter dimensions to fractional inches.
I would say that in 1963 when the spec was made (possible from an older spec)
that decimal inches were rare and not popular and it was common to express all
(or most) inches in fractions. So, how do you convert a rounded metric number
to a fractional inch and then come up with a usable fractional size that is in
either 16-ths or 32-nds? Anything smaller is not practical.
302 mm converts to 11.89 inches. The nearest fraction is 11.875 mm
which is 11-7/8 inches. This however is only 301.625 mm. The reason for the
asymmetrical tolerances is to accommodate rounded numbers in both units, the
302 mm in metric and the 11-7/8 in inches. If we add the 1/32 tolerance to
301.625 mm we get 302.42 mm. The average of the two is the 302.02 mm you
noted, which for all practical purposes is the 302 mm intended. However, in
inches there is no common fraction to equate to 302.02 mm. So the closest
common fraction was chosen and the tolerance was made asymmetrical.
If the RIAA spec were ever to be updated it could simply drop the
0.02 mm extra you noted and simply make it 302 mm +/- 0.4 mm. Would you agree?
I do find it interesting that the RIAA wanted their records to be an
extra millimeter in radius bigger then the standard 300 mm. Could be they
wanted to have extra leader space at the beginning.
As a side note I wonder if the 1963 spec was an update to an earlie
spec and how far back the spec really goes? If so, and the inches were in fact
not post 1960 inches, then how would pre-1960 inches or even pre-1900 inches
affect the outcome of the conversions?
At least we now know that the dimensions are what is intended and
that the reference to shrinkage is just wishful thinking.
It just goes to show that the extremist propaganda that claims
everything in the past started out as inch based is wrong and that there are
many examples that actually started out as metric based and were later
corrupted by the English world in inches and the metric history was forgotten.
It is time to revive the truth about products that originally were metric to
begin with.
Jerry
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