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
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