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Message-ID: <5.1.0.14.0.20020225164111.00a837c0@gemini.herts.ac.uk>
Date: Mon, 25 Feb 2002 17:18:32 +0000
To: rsgb_lf_group@blacksheep.org
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Subject: RE: LF: Spelling of units
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Dear LF Group,

A lot of the variations on symbols for units seem to be due to computers; 
for instance, most CAD and simulation software can't do Greek letters and 
is not case-sensitive. The Pspice simulator that I use at work a lot 
interprets a resistor of either 1m or 1M as 1 milliohm - you have to put 
1meg if you want a 1 megohm resistor. Confusingly, while 4.7k gives what 
you would expect, it will interpret 4k7 as 4 kilohms, and ignore the 7. 
Fortunately, 'u' is not used in many units, so uF has fairly obvious 
meaning. Also, the word processor I use puts nasty red lines underneath 1 
mA, but seems to approve of 1mA - perhaps it is American influence at 
work!  I think the use of * to indicate multiplication stems from many 
types of computer languages which use this notation to avoid the ambiguity 
possible if 'x' or '.' were used instead in a text-only display.

The standards bodies seem to have been determined that we should use the 
new logic symbols for a couple of decades now - engineers around the world 
seem equally determined not to use them! The resistor symbol is a bone of 
contention too, with many still preferring the zig-zag line over the 
rectangular box.

Some old American books seem to use 'M' for ohms - so there are lots of 
50,000M resistors marked on circuit diagrams, which looks a bit strange...

Cheers, Jim Moritz
73 de M0BMU