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From: mmar@sphinx.UChicago.UUCP (Mitchell Marks)
Newsgroups: net.misc
Subject: multiplier legend on dials & meters
Message-ID: <1471@sphinx.UChicago.UUCP>
Date: Tue, 24-Dec-85 22:13:13 EST
Article-I.D.: sphinx.1471
Posted: Tue Dec 24 22:13:13 1985
Date-Received: Sat, 28-Dec-85 01:08:27 EST
Organization: U Chicago -- Linguistics Dept
Lines: 60

Subject: multiplier legend on dials & meters
Newsgroups: misc
Distribution: net

[Naw, I don't really believe there's a line-eater.]             really believe there's a line-eater.                                    



Can anyone explain the rationale for the explanatory legend that goes on a 
dial or meter when the actual numbers shown represent some fixed multiple 
of a standard unit?  It seems to me that they often have it exactly 
backwards.  

I'll use a tachometer in a car as the example, though you can see this 
lots of places.  The numbers printed on the dial are just 1, 2, 3, 4, etc,, 
to indicate 1000 RPM, 2000 RPM, 3000 RPM, etc.  (Some of them may show the 
number in full, but no matter: we're considering the case where they 
abbreviate.)  Then somewhere on or near the dial you'll find a notation 
like this:
               RPM X 1000

But that's not right!  Suppose the dial says 3.  Then

               RPM X 1000 = 3
               RPM = 3/1000 = .003

In other words, your engine is turning over at .003 RPM.  Well, that's 
obviously too low (by a factor of a million).  Let's work it the other way.  
Your engine is turning over at 3000 RPM, what should the dial show?

               RPM = 3000
               RPM = 3 X 1000
               RPM/1000 = 3

That is, when the dial shows 3 to mean 3000 RPM, the 3 indicates the actual 
rotational frequency of your engine (in RPM) *divided* by 1000, not *times* 
1000.   (I should have said earlier that I've been writing RPM not for the 
unit, but as a variable meaning "rotational speed of the engine measured in 
RPM", which seems the sense involved in the notation RPM X 1000.)

The alternative I seem to be supporting above is that the notation should 
be instead

             RPM / 1000

but there would also be nothing wrong with

              1000 RPM(s)

which works quite differently from RPM X 1000.  The legend 1000 RPM would 
mean "this dial shows the rotational speed of the engine, measured in units 
of 1000 RPM".
 
Okay, okay, so everybody does it that way.  But will you explain clearly 
where I've gone wrong, if they're right?

-- 

            -- Mitch Marks @ UChicago 
               ...ihnp4!gargoyle!sphinx!mmar