Imagine travelling to a city to buy a length of cloth to make a dress. You know you need 8 metres for the pattern and so when you visit the cloth merchant, you ask for 8m of the finest cotton which he cuts and puts in a paper bag. You then go back to your home in the village 100 miles away, open the bag and find that you have only 7.2m. It is to long a journey to go back and so you have to make a smaller dress and breathe in to wear it.

Strange? Well, hundreds of years ago this could have easily been the case.

You wouldn’t have used metres as units, you might have used yards or ells (derived from elbows), bolts or barleycorns!

Sometimes, even though the different areas of the country used the same word for the unit or length, they could actually differ.

A similar story would also be the case for trading masses of flour, spices and other materials. Numerous arguments and fights would ensue from people thinking that they were being short changed, caused by the lack of consistency between units of measurement.

This was certainly the case after the French Revolution, where the French thought that it would be a good idea to standardise units of measurement, to avoid such conflicts. The standard metre was therefore born, similar to the British yard, just a bit bigger. A metre bar, made from a platinum/iridium alloy, was kept centrally and people would have their own metre stick made from this standard. There was a similar block made for the standard kilogram.

Phew, that’s better, now quantities could be compared more fairly.

Across the channel in Britain and in many other countries, there was another problem: multiples of different quantities appeared to make little sense and had just been derived from quantities that seemed useful at the time. For example for mass:

There were 16 ounces in a pound, fourteen pounds in a stone and 160 stones in a ton.

For length:

There were 12 inches in a foot, 3 feet in a yard, 22 yards in a chain, 10 chains in a furlong, 8 furlongs in a mile and 1760 yards in a mile.

The coin system again had different multiples. YOU had to remember each and every one!

In 1960, when it was becoming more and more crucial to keep units standard, the System International d’unites was set up. Known as the SI system, it was adopted nearly world-wide (the Americans weren’t that keen!).

In the SI system, alongside the use of standard units, one of the rules was that any multiples of units, must use powers of ten.

As bigger and bigger measurements were needed names were given to particular powers of ten, each one being 1000 times bigger than the previous unit. Similarly smaller and more precise measurements were becoming important and so again names were given to units that were one thousand times smaller than the previous. Prefixes such as mega, nano, pico, tera were set to describe these quantities. But what do these words mean and are they fitting?

Well the names derive from words used in different languages to describe size.

Think of some of the words in English used to describe size: tiny, diddy, little, small, medium, large, massive, huge, gigantic.

Let’s take a closer look at the SI prefixes, starting with those that get smaller and smaller.

Well first there is milli, as in millimetre or millisecond. This comes from the Latin, mille, for one thousand and the milli prefix means one thousand times smaller (or x10^{-3}). So 1mm is one thousandth of a metre, 1 x10^{-3}m. So that makes sense.

The next smallest is micro. This comes from mikros, which is greek for small. How small? A million times smaller. So 1 microsecond is one millionth of a second (or x10^{-6}). What is smaller than ‘small’?

Nano- is the answer. This comes from nanos, greek for dwarf. So dwarves, it seems are smaller than ‘small’. Nano- is one thousand million times smaller, or one billion times smaller. So a nanometre is the same as 1×10^{-9}metres.

Pico is the next smallest and less creatively pico is simply italian for small. It stands for x10^{-12} of the original quantity or one million millionth. So it appears that what the greeks considered to be small was in fact one millon times bigger than what the italians thought was small. Think of the implications!!

Let’s now go bigger. One thousand times bigger than a metre is the kilometre and one thousand times bigger than a gram is a kilogram. So kilo- represents one thousand times bigger (or x10^{3}). Kilo comes from, khilioi, the greek for, guess what?! One thousand.

Mega is the next one up, representing one million times bigger (or x10^{6}). Mega derives from the greek word for GREAT, megas. We seem to have adopted this in common parlance. That’s mega, mate. Ie that’s great!

A billion times bigger (or x10^{9}) is the prefix giga. For example 1 gigahertz is one thousand million times faster than 1 hertz. Giga is from, gigas, greek for giant.

And finally, my favourite, tera. Tera stands for one million million times bigger than the original quantity (or x10^{12}). And where does tera come from? Again it’s greek and it’s from teras, which means MONSTER!

So monsters are bigger than giants which are bigger than ‘great’ characters and all are bigger than dwarves!! We knew that…

So what’s the age of the universe? Well we think at the moment it is about 13.7 billion years old and this equates to:

5 monster days or 5000 giant days or 5000 000 great days….. How cool is that?