In a message dated 2/25/02 12:25:57 PM Eastern Standard Time,
[email protected] writes:
<< 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. >>
Interesting point, Jim. I suspect most of that has to do with the computer
programmer's personal preferences, however, rather than any limitations of
the computers themselves. I cannot think of any modern operating system or
language that is incapable of distinguishing between uppercase and lowercase
letters in string variables. While CAD and simulation developers may value
backward compatibility with early 4- and 8-bit microprocessors having limited
display capabilities, surely there must be limits to such a noble notion!
(grin)
Even the 4k7 versus 4.7k distinction reflects the programmer's bias, rather
than a hardware or software necessity. It takes no more than half a dozen
lines in most high-level programming languages to recognize a "word" having
the form digit-letter multiplier-digit as being equivalent to
digit-decimal-digit-letter multiplier, and converting it to the same
numerical value for computation.
<< 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! >>
Actually, we Americans are just following RadCom's lead on this. :-)
In reality, it's not clear to me why a word processor should observe any rule
on this at all, but you are right about some of them doing so. Very odd,
considering that in the past few days we've seen on this reflector that
national standards bodies do just the opposite. Perhaps RadCom's usage is as
VK7RO says...publications don't want to have the numeral(s) appear at the end
of a line and the unit at the start of the next line.
Ironically, this is one of the points where a computer program like PSpice
would find it easier to have no space between the value and the unit. If an
application clearly sees "4.7k" or even "4k7" in a list, it can simply
disregard all blank spaces and doesn't have to employ quite as large an
algorithm as if it had to also make the determination that "4.7 k" means the
same thing too.
<< 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. >>
I would agree that's probably why it is so common. In typesetting and in
reasonably advanced maths software, fortunately, we have less ambiguous
symbols for indicating the product of two expressions. But since there are
no ordinary keyboard equivalents, we have to make do with what's available.
<< 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. >>
Guilty as charged.
<< 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. >>
Hmm. I'm rather fond of old American electronics books, and can't say that
I've encountered this peculiarity. I wonder if it could result from a
technical draughtsman's misreading of the author's hand-scrawled omega.
Or--could it possibly be that, far enough back in the dim mists of early
radio, "mille" was an acceptable prefix meaning 1000, before the less
ambiguous Greek prefixes became the norm? Is anyone on this list both old
enough, and willing to admit to it, to remember for certain?
73,
John Davis
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