Why are currency conversion quotes the wrong way round?

Reply to
Norman Wells
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That's wrong. The correct formulation is:

speed = 60 * miles / hour or in the posh scientific form:

speed = 60 miles.h**-1

speed has dimensions length * (time**-1)

miles has dimensions length

hours has dimensions time.

If you you multiply both sides by hours, you get

speed * hour = 60 * miles

which is not very useful, but if you then divide both sides by miles, you get:

speed / miles*(hours **-1) = 60, the left hand side of which is basically how a physicist would label an axis of a graph express in speed in imperial units. (With the right units and typesetting, it would be more like speed / ms-¹.)

miles/hour` is completely wrong as you are equating a pure number wit h something that has two dimensions.

Reply to
David Woolley

Obviously it's wrong - that was rather my point. To make it work we'd have to read it as something like: "the cost of driving 1 mile divided by the cost of driving for 1 hour" AND we'd need to equate that to the *inverse* of what mph is commonly interpreted as, giving us

mph = 1/60.

Which now of course makes perfect sense!

Personally, when I see a column of numbers headed mph or £/$ I'd prefer to be able to interpret those numbers consistently, but it seems that economists like to do things differently.

Thanks Thomas

Reply to
Thomas

The "/" symbol can have two totally different meanings. One is "divided by", the other is "per". They are not the same at all.

Reply to
Chris Blunt

Oh, I think the "/" can have lots of meanings and interpretations and I'm perfectly happy to read 3/5 as 3 divided by 5. When the two items separated by the slash are in different units however, I think the obvious interpretation is "per" . And per is really an implied division - mph is just the number of miles divided by the corresponding number of hours. Speed, the cost of spuds or the exchange rate are most naturally (imho) expressed in this way.

For economists to decide to interpret an exchange rate expressed as £/$ as "the value of one pound divided by the value of one dollar" seems perverse and confusing to me.

But clearly the convention is here to stay.

Thanks Thomas

Reply to
Thomas

In article , Thomas wrote: }Personally, when I see a column of numbers headed mph or £/$ I'd prefer to }be able to interpret those numbers consistently, but it seems that }economists like to do things differently.

No. They're exactly the same. Given something like GBP/USD, convert both to a common value (e.g. EUR, giving 1.3877 / 1.0731 currently) and divide them. Just as mph, or miles/hour, means miles divided by hours, GBP/USD means GBP divided by USD.

Reply to
Charles Bryant

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