Originally, there was the 12 oz, 480 grains per ounce troy system. For commerce, it was decided that a larger pound was required. Thus the mercentile pound of 15 troz (7200gr). However, binary was decided to be better and, let's face it, 15 is a pretty rubbish number. So was born the 437.5 gr ounce and the 7000gr pound. Could someone answer me this question, please?

Why wasn't a new ounce just mmade 15/16 troy ounce (450gr), with 16 to the pound (thereby keeping the 7200 grain pound). Why on earth was the 437.5 grain ounce devised???

The last things you should expect to find in the imperial system is either rhyme or reason !

There's more of that in the imperial system than in metric (one of many examples would be...let me think... a pint of water weighs a pound and a quarter)

a gallon weighs 10lbs- think of it that way. Also, a floz weighs a floz.

<<
let me think... a pint of water weighs a pound and a quarter
>>

which pint - UK or US.

That is one of the problems with the Imperial system - you need to know the writer's frame of reference. In the metric system, a litre is a litre is a litre regardless of where the writer is.

...but that doesn't rhyme!

Here's the versions:

UK:
A pint of water weighs a pound and a quarter

US:
A pint of water weighs a pound the world over

Other:
A litre of wine will make me feel fine

..erm

..the world over

BTW The phrase in the US is, "a pint's a pound the world around."

Now, as to your question about the pound/ounce. The basis of the system was not the ounce, but the grain, so changing the ounce would have been just as awkward. They held the unit of the grain constant and then redefined all units from that point. 7000 grains was close to the Italian pound unit of the late 13th century and thus was defined as such. The avd. system then worked the following way:

16 drachms/drams = 1 ounce
16 ounces = 1 pound
14 lb = 1 stone
2 stone = 1 quarter
4 quarters = 1 hundredweight
20 long hundredweight = 1 long ton

And for our American readers:
100 pounds = 1 short hundredweight
20 short hundredweight = 1 short ton

Because the avoirdupois ounce is 7000/16 = 437.5 grains while the troy ounce is 5760/12 = 480 grains. There is never a need in the avoirdupois system to use a unit smaller than a drachm and frequently never smaller than an ounce. If things that small are being measured then the Troy system is appropriate.

Conversion between troy and avoirdupois units is so awkward, no one wanted to do it. The troy system quickly became highly specialized, used only for precious metals and for pharmaceuticals, while the avoirdupois pound was used for everything else.

<<
BTW The phrase in the US is, "a pint's a pound the world around."
>>

Now that is a little arrogant - if the average British working man was forced to use US pints in the pub, he would very quickly start demanding that his beer was served by the half litre!

I remember from my imperial school days:

"A pint of water weighs a pound and a quarter, a gallon of water weighs ten pounds."

I also remember doing applied maths problems using that information. At the time I thought it quite handy to remember.

But then I discovered the metric system where a Litre of water weighs a kg. Can't beat that for simplicity. I've never looked back since!

A litre of water only weighs a kg if it is at 4 degrees C and (I think) distilled.

A litre of water at 5 degrees does not weigh a kilo, not does a litre of orange juice, paint or petrol. The linking of a litre to a kg is arbitrary, like all measurement.

Forum Owner wrote

<<
A litre of water only weighs a kg if it is at 4 degrees C and (I think) distilled.

A litre of water at 5 degrees does not weigh a kilo, not does a litre of orange juice, paint or petrol. The linking of a litre to a kg is arbitrary, like all measurement.
>>

1. You are correct about the distilled water part. If there are any impurities, they affect the mass of the water. One litre of Sea water at 4 degrees C, for example, has a mass of 1.033kg. One litre of distilled water at 45degrees C has a mass of 0.99kg and at 100 degrees C a mass of 0.96kg.

2. Orange juice can be considered as being distilled water with a few impurities - it depends on what error is acceptable as to whether or not you approximate the density (and hence the mass of a litre) of orange juice with the density of water.


3. Paint and petrol do not contain water (as anybody with GCSE cheistry shuld know), so we cannot asume that the density of either paint or petrol is the same as the density of water. BTW, the density of petrol is of the order of 0.8kg/litre.


One US gallon of water at 4 degrees C weighs 8.3452 lbs, making one pint 1.043lbs - I think that metric wins on this one!

1. Matts s, that doesn't answer why they didn't make the zavoir/troy conversion simple in the first place by making an avoir oz 15/16 troz

2. There is only one Imperial system.

Thank you.

<<
There is only one Imperial system
>>
Bryan - MattS is an American - they revolted against the Imperial system in about 1776.

They call their system the system of Customary Units (which has a large overlap with the Imperial System - pounds, ounces, miles, yards, feet and inches are the same; gallons, pints, fuid ounces, hundredweights and tons are different; stones are not used in the US while dry pints are not used in the UK)

Martin:

"if the average British working man was forced to use US pints in the pub, he would very quickly start demanding that his beer was served by the half litre! "

Of course if you've been to the US you will know that you are talking rubbish.

"Pubs" in the US regularly serve what I've seen called a "real pint" - 20oz. Also if you go to an "Irish" or "British" pub in the US you'll get the full 20oz if you ask for a pint.

If you go to an all american bar you can get rid of any confusion by simply asking for a 20oz glass of beer.

This is from my experiences in america.

It was also nice to be asked my age - made me feel "young"!

Well, I have never been to America so I was unaware that tehy have two different pints there. I have however been to 13 countries in Africa, 1 in Asia, 1 in the Indian Ocean and 15 in Europe. All these countries apart from the United Kingdom and Eire use the metric system almost exclusively.

Bryan,

As I said before, they were not interested in making the conversion easy. They were trying to match an already in use unit in Italy, which at the time the avd. pound came into being was a European power. They created the 7,000 gr. pound and then divided it into 16 ounces, and were not interested in relating it to the troy pound at all. Remember, the base unit was the grain, not the ounce. It was all created completely independantly of the troy system. They found a weight that they liked, and then reproduced it in grains and then divided it into 16.

As for our American Customary System of Weights and Measures, it's actually older than your Imperial System. The standards for the American volume measures which differ from the Imperial ones are:

The Queen Anne Gallon which was called the Wine gallon of 231 cu in. This was defined by your Parliament in 1707
The Winchester Bushel was defined by your Parliament in 1696 defined as the volume of a cylinder 18.5"x8"

Your volume measures were created in 1824 because of a ghastly fire at the Royal Observatory at Greenwich. The Americans still had their copies of standards and instead of reverting back to the older measures, your Parliament made new ones.

As for the US, there was a push in the very early part of our history to move to a decimalized system of weights and measures to match our decimalized dollar. The system was created by Thomas Jefferson before the French metric system. However, once the national land survey began in the late 1790's, the land got measured in feet, chains, and acres and the fate of the metric system and Jefferson's system in the US was sealed.

MattS wrote

<<
As for the US, there was a push in the very early part of our history to move to a decimalized system of weights and measures to match our decimalized dollar.
>>

I remember reading somewhere that in the very 1800's the US government acquired a copy of either the standrd metre or the stadnard kilogram from Napolean's Governemnt in France but the ship that was carrying it over to the US sunk in a storm.

Matt (or anybody else) can you confirm this?

I am well aware of that a litre of water only weighs exactly 1 kg under carefully defined conditions. Though for most practical everyday purposes the discrepancey is negligible.

I always note with amusement that nobody on the anti-metric side bothers to mention this when it comes to the imperial version.

At the time Jefferson was working on his decimalized system there was indeed a copy of the Meter and a copy of the Kilo sent and the ship didn't sink, but had to make a change of course. The man carrying the copies (his name escapes me) was then arrested in the Carribean for some crime and was detained there for a period of time. His copies were confiscated. They were later auctioned off and somehow made it to the US Government. By the time they did (about 1810), the US had all but abandoned it's attempts to adopt any decimalized measurement system. The copies survived to this day at the National Institute of Standards and Technology (NIST).

The entire history of the US Measurement Systems is detailed in the book I have oft mentioned called Measuring America, by Andro Linklater

Pip,

A British fluid ounce of water weighs an ounce. Very simple. No worse than the fact that a millilitre of water weighs a gram (I can't help but notice that a litree of water weighs a kilo and a millilitre of water weighs a gram - wouldn't it be more convenient for you if the gram was a thousand times heavier? - a fuldamental unit ought not to be a kilo-anything)

1 fl.oz water weight 1oz
1 pint water weighs 1.25 lbs
1 gallon water weighs 10 lbs
No other fluid measures are in common use in the UK.
Ratio of largest unit to smallest unit is 1:160

In contrast
1 ml water has mass 1g
1 litre water has mass 1kg
1 m^3 water has mass 1 tonne
Ratio of largest unitto smallest unit is 1000000:1

Thus there is a 1:1 ratio between the three most common metric units, but a 1:1 ratio with ine one Imperial unit. Moreover the span of measurements covered by these metric units is 6000 times as large.

Metric 2 Imperial 0.

However the score should be:

Imperial 49300000 Metric 8700000

When based on number of people who actually use the damn measurement systems.

Naturally I prefer that score!

Anyone been watching "diet trials" on BBC1?

"1 fl.oz water weight 1oz
1 pint water weighs 1.25 lbs
1 gallon water weighs 10 lbs
No other fluid measures are in common use in the UK.
Ratio of largest unit to smallest unit is 1:160

In contrast
1 ml water has mass 1g
1 litre water has mass 1kg
1 m^3 water has mass 1 tonne
Ratio of largest unit to smallest unit is 1000000:1"

Who cares? I sure don't. Since when am I worried about how many relationships I can make? If I want a good approximation I only remember that 1 pint=1 lb (since I'm an American). If I need detailed calculations, how difficult is it to remember that there is 62.4 pounds/cubic foot or that 8.33 lb/gal. I use the things everyday. Big deal. It's just a number to remember.

One thing I do know is the following thing. Your standard metric units of volume are *absolutely* inconvenient. The cubic meter is too big for good engineering computations and the liter is too small. Your metric system has nothing on the convenience of scale of the gallon (US or Imperial) or the foot.

I say for convenience in scale of size, Customary Wins.

Metric 2 Customary/Imperial 1

There is another aspect to this. The litre is a direct expression of cubic linear measure (1000 cc or 1 cubic decimetre). Which is more logical since it is a measure of volume.

This is not so with customary or imperial measures. In the British case a pint is 34.7 cubic inches (approx) and the gallon is 6.2 cubic feet. There is no deliberate connection.

One more point to metric.

There is no apparent connection because there was never meant to be a connection. Gallons are for measuring quantities of water based upon an amount deemed reasonable to the human being. 1 gallon is from the Latin for pailfull. We use pails and buckets everyday in household measures. How convenient is it then to have a unit that we can all relate to? 1 gallon is an extremely convenient unit for measuring liquids we use everyday. Again, the liter is too small. Who uses a wash bucket that's 1 liter? My mother uses one which is 1 gallon. That's a convenient amount of water to carry and does the job on the kitchen floor.

If you want cubic volumes, nothing is stopping you from using cubic inches, feet, or yards. In fact, the standard measure for flow in Civil Engineering applications is the cubic foot per second, which in the US is abbreviated cfs and in the UK the cusec. The meter is too large for use in this manner. 1 cubic meter per second is a massive quantity of water too large to quantify normal flows in natural situations.

What a load of old rubbish, MattS.

If you're designing a surface water drain for a single house or office building l/s is a perfectly reasonable unit to use.

Similarly, if you're designing a sewer network for a 1 in 60 year storm then m^3/s is also a perfectly reasonable unit to use.

In fact, both of these units are so reasonable that they have been used by British Engineers for the last thirty years without problem !

Actually, the gallon is pretty much too big for anything but water. Unless you live in a large household, a gallon of milk always turns bad before you can finish it, soda turn stale.
A liter is much more convenient and enjoys growing popularity here in the US.

Ralf

<<
In fact, the standard measure for flow in Civil Engineering applications is the cubic foot per second
>>

This is rather a sweeping statement - it might be the norm in the US, but is not the norm in the UK. In 1980 infact I was involved in converting a computer system in the water industry from Imperial to Metric units.

Furthermore, within the European Union it is a legal requirement that any government job with a value of more than 100,000 Euros (a little over $100,000) is put out to Europe-wide tender. Another European Union regulation requires that the metric system be used for all legal purposes except those that are subject to international agreement (such a heights of aircrfat) where non-metric measures are used. This shows you very much that in Civil Engineering outside the Untied States, cubic metres per seconds rather than cubic feet per second is the norm.

Ralf: Add to your list - petrol is better in gals too considering we all know our cars' mpg figure.

<<
we all know our cars' mpg figure.
>>

... but your mpg figure will be different to MattS's mpg figure (assuming that you drive identical cars). However, my l/100km is the same the world over.

Since petrol is now dispensed in the UK by the litre and you have to do one conversion to get either mpg or l/100km, isn't this an ideal opportunity to get used to l/100km?

"Unless you live in a large household, a gallon of milk always turns bad before you can finish it, soda turn stale."

That's because you Brits use a goofy gallon that's 0.2 times too large. If you had stuck to your Queen Anne gallon instead of royally screwing up the system, we'd all be in good shape.

"Another European Union regulation requires that the metric system be used for all legal purposes except those that are subject to international agreement (such a heights of aircrfat) where non-metric measures are used. This shows you very much that in Civil Engineering outside the Untied States, cubic metres per seconds rather than cubic feet per second is the norm."

The only reason it is is because the rest of the world was forced to metricate. Just because the European Union says so is not a good argument for the superiority of the Metric System.

I find it entertaining that all the metricators resort to arguing that it's required by the European Union when their beloved system is questioned.

Saying that the metric is required now and we should switch our mpg figures to l/km figures is no argument for why metric is better. Metric will always look better when you say that since everything is in metric, that things would be so much more convenient in metric.

METRIC IN THE US IS INCONVENIENT. Why? Because hardly anything is in metric. That makes it inconvenient. See if you can present an argument on the superiority of metric without referring to the fact that it's required where you live.

"... but your mpg figure will be different to MattS's mpg figure "

What on earth are you on about? I only want to know my mpg - why should I have sleepless nights on the mpg of a person living in a country where I don't drive a car (except when on holiday)

bad argument

MattS wrote:

"That's because you Brits use a goofy gallon that's 0.2 times too large. If you had stuck to your Queen Anne gallon instead of royally screwing up the system, we'd all be in good shape."

You realize that I *was* talking about the US gallon, since I live in the US ?
The 20% more volume of the UK gallon doesn't really matter, both the UK and the US gallon are just too huge for anything but water !

Ralf

Measuring the amount of fuel a vehicle uses in L/100 km is more sensible than mpg for two reasons.

(1) Generally, when we buy fuel we wish to make sure that we have enough for the forthcoming journey(s). In other words we start with knowing the distance and then work out the amount of fuel required.

For example if my car uses 8 L/100 km and I expect to travel 250 km then I'll need 2.5 * 8 = 20 L.

In mpg (British) this translates (roughly) to 35 mpg and 150 miles. So to get the amount required in gallons that's 150/35 = 4.3 or about 4 an arf gallons.

Of course in Britain I would then have to convert to L because petrol isn't sold by the gallon.

For my money the L/100 km is easier (mentally) because it involves multiplication rather than division (except by 100 which is trivial) by relatively large numbers.

(2) mpg is NOT a measure of consumption - it is the inverse of consumption. Cars don't consume miles!

Pip wrote

<<
mpg is NOT a measure of consumption - it is the inverse of consumption. Cars don't consume miles!
>>

I agree - moreover, X litres/100km easily converts to £Y/100 km - a direct cost of the petrol component of motoring.

If you put in ten gallons and your car does 40 mpg then the tank will take me 400miles

Blimey - that was rocket science!

Anyway, since your lot (Pip,Martin's) forced us to use litres most people put in "20 quids worth" rather than "so many gallons" thus destroying a way of speech in the process. And, of course, it now takes the likes of the TV and papers to warn us of when we approach £4/gallon rather than notice this on the forecourt.

Of course, you will be proud of this.

Well done Steve. Your example shows how easy it is to multiply and divide when factors of ten are involved. You're learning!

As for the other busines I can promise you that I and am sure other pro-mets had nothing to do making you buy petrol in litres, the retailers did that all by themselves. They prefer litres for much the sam reason that rebel market traders prefer lbs, its a smaller unit and looks cheaper.

I can further assure you that we do not relish the media persisting with gallons. It isn't rocket science either to realise that a few pence on a litre works out to an extra pound or so on a tank.

The first part of your last sentence heartens me!

BTW - tried to keep the mpg/ division by 10 thing simple so that even you metric extremists could understand.

When will your sort ever understand that the human naturally and instinctively uses the best measure for him at the time of application? Whether it be a millimetre or a mile?!?!

I feel quite sorry for you really since your argement will never win.

I need to ask - would you like to see laws that make it difficult for the media and "the man on the street" to use his preferred words that include "inch", "yard", "pound" etc and if 'yes' how would you enforce it?

Please answer this honestly rather than hide behind some "evolutionary" theory of imperial dieing off eventually.

The normal way of expressing the cost of something is to do so by quoting the cost of a single unit of benefit. If I am buying a jar coffee, the unit of benefit is one jar of coffee, so the cost is £2.50 per jar. If I am buying bananas, one unit of benefit is one kilogramme (one pound in Sunderland). The cost is then expressed in pence per kilogramme.

When you are expressing the cost of motoring, the benefit is 1 unit of distance travelled, whiel the cost is how much you paid to travel that distance. ! unit of benfit is 1 kilometre (or 100 kilometres or 1 mile etc). The [petrol} cost of the journey is how much petrol you used to travel that kilometre, 100 kilometres, mile etc. The early motoring enthusiasts introduced mpg when they were boasting how far they could go without filling up. They were wealthy men (and women), so the cost did not really bother them. Today the average motorist is more cost concious so using mpg is a bit of a nonsense. After all, why should the cost of petrol double when the mpg halves?

I'm shouldn't even touch this argument. It's so useless and base, that it's not worth my time.
BUT....
Let's just say that when I fill my tank, I watch the dial read how many gallons I put in. I then take the reading on my tripometer and divide it by the reading on the gasoline pump. It's NOT THAT HARD!

~280 miles on the trip
~10 gallons in the tank
~28 mpg

And for those of you who don't like base ten

~300 miles on the trip
~12 gallons in the tank
~25 mpg

I happen to like the inverse of consumption because it tells me how far I can go for an amount of gasoline. If my car does about 30 mpg, then when my tank gets low and I have about 2 gallons left, that tells me that I can go about 60 miles (or an hour on the expressway) before I run out of gasoline.

I atually find the metric way of working it (fuel consump) out rather bizarre - a bit like over 97% of British motorists.

Also Martin - I wasn't aware that I live in Sunderland here in the deep south east! Whenever I've seen bananas sold i've seen "per pound" only (ooh! tut tut!) or a mixture of "per pound" and "per gramophone" (or whatever its called). Can you honestly tell me a place where loose bananas are sold in metric only? Please desist lieing on your reply! I'll give you a tick list to get you going:

Tesco (ahem!)
Safeway
M&S
Somerfield
Morrisons
Asda (fuel price shown in gallons)
Sainsbury
Waitrose
"The small corner shop"
Shop Francais (joke)

Steve,

Just because we prefer metric for its decimal structure and proclaim it to be easy does not mean that it represents the limit of our understanding.

People use units they feel appropriate for the task sure, as to whether thay are natural that depends what you mean by it. Sometimes people need pursuading that its better in the long run to use units from the same coherent system rather than mix them up with ones that are totally incompatible involving awkward conversion factors.

As for winning, there are seldom any real winners when people argue from entrenched positions. All we can hope for is a healthy exhange of views.

No I don't advocate laws of the kind you describe. The laws that do exist to control the units used for trade and official purposes are adequate, its just that some people need to be convinced that they should be applied in fairness to everyone else.

As for your last point let me assure you I always give honest answers.

I'm intrigued by your line:

"Sometimes people need pursuading that its better in the long run to use units from the same coherent system rather than mix them up with ones that are totally incompatible involving awkward conversion factors"

I'm from a generation that has grown up with both systems. Ok, unfortunately during the 80's the "system" (those in authority) thought it would be trendy to drop all teaching of imperial (only to be brought back in the 90's) so if you like I should be a metric robot more than anything else.
Considering your point I must be very ignorant to "pick up" this system outside my education (ie imperial) and find it preferable in most things?

If you say anything about "habit", "old people" or "family pressure" then I will have to walk away from this discussion - much in the same way as anyone would walk away from an unscalable brick wall.

(Unless you really believe that my mental intellect is sub-zero, that is)

1. I know the history- my point was "wouldn't it be interesting to make a pound 7200gr"

2. A correction- the fluid ounce is not the smallest imp unit- the minim is (1/480floz)

As I have learned more about metrology since I posed this question, I have kind of found my answer:



It would appear we originally- in Saxon times- used the Tower pound of 12 450 grain ounce (5400gr). 15 of these ounces and 16 of these ounces (6750gr & 7200gr) were also used as standard units at tiems, along with the troy pound of 12 480 grain ounces. In short, we could easily have ended up a 7200 grain pound.