Re: [boost] [Review][PQS] Review deadline

From: Paul Giaccone (paulg_at_[hidden])
Date: 2006-06-07 10:16:47

Reece Dunn wrote:
> Gerhard Wesp wrote:
>   
>> Conversion factors between non-SI units and SI units should be constant
>> dimensional quantities, e.g. (assuming constructors from double):
>>
>> const length foot                 =    .3048 ;  // Meter
>> const power  european_horse_power = 735.4987 ;  // Watt
>> const mass   pound                = 0.4535924;  // Kilogram
>> // ...
>>
>> This way, one could e.g. construct dimensional quantities like this:
>> const power deux_chevaux = 2 * european_horse_power;
>>     
>
> However, if you are working in *pounds*, and you want the *result*
> in pounds (e.g. how many pounds of flour do I need to order?) then
> you are going to end up with the result in kg!!
>
> Also, in Britain we are still using miles per hour (despite having converted
> to metric a long time ago!). Therefore, it would be silly to answer the
> question "how fast do I need to travel to get to work in 10 minutes?"
Actually, it's worse than that. The UK began metricating in the 70s 
after decimalising its currency, but never actually finished the job. As 
a result, we are in a sort of limbo where both systems are in use. For 
example:

* petrol (gasoline) is dispensed in litres, a fairly recent change, but 
people still talk of miles to the gallon (rather than kilometres to the 
litre)
* fruit and veg must be sold in kilos although may still be priced in 
pounds as long as they are also priced in kilos; many market 
stallholders still sell them in pounds, which is technically illegal, 
and some have been prosecuted;
* road signs still give distances in miles and speeds in miles per hour, 
and there are no immediate plans to change this;
* schoolchildren are taught the metric system but not the imperial (aka 
British) system, but most Britons still talk of inches, pounds, etc, so 
everyone ends up needing to know both systems and how to convert between 
them;
* SI units are the only officially sanctioned units in scientific usage

So including imperial (or even just non-metric) units is, I would say, 
quite important, not least because these are the official standard in 
the US. Just to complicate matters further, some units, for example the 
gallon, are different in the US and UK. Then of course there is 
avoirdupois and troy weight...

Someone mentioned spelling variants: note there is also "liter/litre" as 
well as "meter/metre" (and their multiples and submultiples).

Paul