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# Difference between revisions of "Numbers - how to write them"

## Background

We get quite a lot of questions from students regarding various prefixes like mega, giga, etc. What do they stand for? What symbol should we use?

It's rather easy to make mistakes with the symbols for the prefixes (and I'm sure you can find tons of such mistakes here on the wiki). But if you really want to know, we'll list a few here (and this time we'll be careful to make it right).

The SI system uses a lot of prefixes for unit quantities, and we'll present a few of them here:

Name Symbol Base 10 As a number Short scale name
peta P  1015 1 000 000 000 000 000  quadrillion
tera T  1012 1 000 000 000 000  trillion
giga G  109 1 000 000 000  billion
mega M  106 1 000 000  million
kilo k 103 1 000  thousand
hecto h 102 100  hundred
deca da 101 10  ten

## What can go wrong if you write numbers the wrong way?

The following amounts (research funding that our appartment applied for) where published on a university website. On the same page. Take a few seconds to think about how much money (Swedish Kronor, SEK) the following stands for:

• `SEK 3 181 million`
• `SEK 1,998 million`
• `SEK 5 994 million`
• `SEK 11,605 million`
• `NOK 1868 million`

Can you find any inconsistencies?

Let's start with the magnitude of the amounts. How likely is it that a researcher has applied for `SEK 11,605 million`? That's `SEK 11,605,000,000` or SEK 11.605 * 109 or more than 11 billion Swedish kronor (Swedish: mer än 11 miljarder kronor).

What are the recommendations for writing large numbers in English? We don't know if there are competing recommendations, but we'll stick with the recommendations from Uppsala University.

Use comma as a separator between thousands: `1,000`, `10,000`, `100,000`, `1000,000` .

Of the quoted amounts on the page we found, there's actually only two amounts that are written correctly (disregarding the fact that the amount is off by a factor of one thousand). That's `SEK 11,605 million` and `SEK 1,998 million`. Eleven thousand six hundred and five million, so the comma comes after 11, and 1 thousand nine hundred and ninety-eight respectively.

`SEK 3 181 million` and `SEK 5 994 million` are wrong, because they use a space as separator of the thousands instead of a comma. Correct would be `SEK 3,181 million` and `SEK 5,994 million`

`NOK 1868 million` is wrong, because it doesn't use any separator at all. Correct would be `NOK 1,868 million`

But it looks a bit confusing to say even `NOK 1,868 million`. We have a name for that number, `NOK 1.868 billion` (US, Eastern Europe, English Canadian, Australian, and modern British) or `NOK 1.868 milliard` (in Western, Central Europe, older British, and French Canadian), but then we must keep in mind that a point is used as a decimal separator while a comma is used as a separator for thousands. Perhaps `NOK 1,868,000,000` is easier? At least now it is clear that the amount is way too high.

For Swedish readers, it is a mess that there are two English words for 1,000,000,000 - billion and milliard. In Swedish, the word is "miljard".

The number 1,000,000,000,000 is called ...