Re: Deane Kidd and the Metric System

n4buq

I worked in a metric shop for 10 years. I pretty much always used 25.4 as the conversion factor. 0.03937 is a rounded recriprocal of 25.4 which is technically the correct conversion factor between inches and millimeters (and easier for me to remember).

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Tom Jobe tomjobe@gmail.com [TekScopes]" <TekScopes@yahoogroups.com>
To: TekScopes@yahoogroups.com
Sent: Thursday, December 14, 2017 6:36:53 PM
Subject: Re: [TekScopes] Deane Kidd and the Metric System

That is a very neat trick... but consider this simple plan:
For the fractional part of the dimension, divide the bottom number into
the top number to get its decimal equivalent.
Example   (7/16" = 7 divided by 16 gives you 0.4375 inches)
If there are whole inches involved in the measurement then it becomes
1.4375, 2.4375 etc.
Divide the decimal inch number by .03937 and you have your millimeter
equivalent.
Example ( our 7/16" is 0.4375 decimal inches, we divide it by .03937 and
we have our answer of 11.11125 mm.
Memorizing the number .03937 solves the whole problem going either way,
to or from inches and millimeters.
Let's have an example of going from millimeters to inches:
If you multiply 100mm by .03937 you will get it's equivalent in inches,
100 x .03937 = 3.937 inches.
The number .03937 is simply how many inches are in one millimeter.
This .03937 method was the common way that millimeters and inches were
dealt with in shops I worked at in the US.
tom jobe...

On 12/14/2017 4:02 PM, 'Craig Sawyers' c.sawyers@tech-enterprise.com
[TekScopes] wrote:

On the topic of conversion between Imperial and SI units of length
there is a well known method of
quickly converting aliquot parts of an inch to millimetres using the
approximation 254 = 256

If you have a fractional inch dimension, multiply top and bottom of
the fraction by two repeatedly
until
the denominator equals 256.? Shift the decimal point of top and
bottom one place to the left.? The
numerator now equals the inch dimension times 25.6, which is the
equivalent number of millimetres
(to less than 1% error)
Ian
Darn, that is a neat trick. I really like simple numerical methods
like that.

Craig

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