I'm guessing you're quite unfamiliar with the metric system. The different types of measurements are defined in relation to one another and are thus easy to figure out, unlike the imperial system where everything is odds and ends.

A kilogram is (almost exactly, but slightly different) to the mass of one litre of water. The force required to accelerate this mass at one metre per second squared is one Newton. One Newton acting on one square metre is one Pascal of pressure. Applying a force of one Newton through a distance of one metre is one joule of energy. This is the same amount of energy in passing a one ampere current of electricity through a resistance of one ohm for one second. One joule per second is one Watt.

If everyone else was using tcp/ip would it be sensible to continue using ipx/spx?

Ask Sony how well security through obscurity's been working out for them.

Every time one of the red countries does business with the grey countries, there's conversion deadweight.

We should all have one currency too, then?

Currency is backed by different governments, and they have different risks, rates of inflation, etc. We're just talking about measuring things.

Actually, that's the reason that most international trade is done in dollars.

Of course not: sovereign currencies have well-known benefits. Multiple systems of measurement are only a hindrance, a friction.

The friction of unit conversion is much lower, though, because they are constant and don't have transaction fees. The number of centimeters per inch or pounds per kilogram is the same today as it will be next month or next year.

...actually NASA proved that kind of friction to be very severe: http://articles.cnn.com/1999-09-30/tech/9909_30_mars.metric_...

Just think that it also could have affected people...