[sdiy] Metric OT rant

Magnus Danielson cfmd at swipnet.se
Mon Aug 12 22:48:52 CEST 2002

From: jorgen.bergfors at idg.se
Subject: Re: [sdiy] Metric OT rant
Date: Mon, 12 Aug 2002 08:08:42 +0200

Hej Jörgen!

> By the way, do you know how an inch is defined? It is defined as 25.4
> millimeters!
> It was defined by the swede C. E. Johansson (http://www.cej.se/), who
> manufactured precision measurement equipment. He found out that there
> didn't exist any really precise definition for the inch. The americans had
> different competing definitions, which weren't precise enough anyway. So he
> just decided that an inch was 25.4 millimeter, without telling anyone. When
> the americans found out, it was too late, as many of them, had already
> bought Johansson's equipment.

You do learn interesting things when you least expect it. Many thanks Jörgen!

Where did you find that info? (I could not find it at C. E. Johansson's

C. E. Johanssons equipment formed the basis for the big scale auto-industry
since when you had coherent measurements you could improve quality of shafts
etc. so that you could make them in large scale and then mount them into cars
without individual adjustment, which was the norm prior to Johanssons entrance
into the field. Henry Ford had a set on display in the entrence so that all
workers would see the importance of accurate measurements and even quality.

In those days it was big money, big big money.

Incidently, the US definition of a meter where in the US Metric Law 1866
defined to be 39.37 inches. This is used as a basis for the US Serveying foot.
However, that has now in practice been abandoned. The GPS system and it's
Geodetic model WGS 84 is inherently metric. Well, anyway, given the US
definition there is a reverse definition of the inch from the meter, but having
an inch to be 1/39.37 of a meter is however less usefull than saying that it is
25.4 mm.

The trouble with the inch was that everyone had their definition. The span was
quite large actually. When the meter came they solved it, they defined one
and made it the agreed norm. Solved many political problems. If you look at it,
the inch where still not exactly nailed to the same value everywhere. The US
and SI Inches are off by 2 ppm. Isn't it annoying?


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