To comma, or not to comma.

I am often asked about commas!

It may seem a strange thing to be asked about (in the maths field), but it is related to the writing of numerals.

If you were asked to write the numeral 1 million, two hundred thousand and seventy, would you use commas?

Would it look like this: 1,200,070?

or this 1 200 070?

Interestingly, your answer most likely depends on where you live (and if I am correct, in the case of Canada, if you speak English or French), and the decimal marker you use!

Over the course of history there has been much debate over how to show where the whole numbers end and the decimal numbers begin. 

Across the world, and through the years, a dot (.) comma (,) and sometimes a line (-) above the ones digit have been used.

As you can imagine this has caused much confusion!

For example, in 1958, the story goes that European and American teams working together on a computer programming language had rather heated debate over the correct representation of the decimal marker, and this threatened to derail the project entirely!

Thankfully a compromise was found and both the comma and the full stop was included! Diplomacy at its finest! 

Whilst down this rabbit hole, I found the following map which indicates how countries currently represent the decimal marker (I love that data is 'unavailable' for Antarctica!- I have visions of people trying to survey penguins about their use of commas!):

By NuclearVacuum - File:BlankMap-World6.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10843055

I find it absolutely fascinating to see the differences across the world- however, I also understand the importance of having some sort of common 'standard'.

In 2003, at the 22nd General Conference on Weights and Measures released Resolution 10 which stated:

the symbol for the decimal marker shall be either the point on the line or the comma on the line,

and also reaffirmed Resolution 7 made in 1948 that:

Numbers may be divided in groups of three in order to facilitate reading; neither dots nor commas are ever inserted in the spaces between groups

Thus, the official international standard is to actually use a space as the 'thousands separator'.

Now, that is the official ruling, but now onto teaching…

I have tried on numerous occasions to teach students to put a ‘space’ between periods (a group of three digits).

However, if you ever tried to teach your students to put a 'space' between their words, or to stand back and ‘give me some space’ you will know that 'space' is quite subjective and your idea of 'space' is often very different to theirs!

So, when I teach students to write large numbers, it have found that it is easier to have them to place a comma between periods. This gives them something to 'do' when they hear the name of the period and avoids issues with the ambiguity of 'space'.

So when I read out the following number, I place special emphasis on the period names as I read... 300 million 456 thousand 207

I instruct them to listen for the names of the periods (million and thousand in this case) and when they hear these, to record a comma.

For example: 300,456, 207

This has worked well for me over the years. 

I always have discussions with students around the fact that the international standard is to use spaces, however I explain that we are using commas to help while we learn this skill. 

The students actually find it fascinating to consider that different countries have different decimal makers. I love sharing a photo from a supermarket in Portugal (see image at the top of this post) where I was so interested by the use of commas as the decimal marker!

So, this week I encourage you to have a discussion around the writing of numbers with your teaching team.

How are your colleagues teaching this- are they using commas, or not? Do they know the international standard? and importantly, do they know what the penguins might be using in Antarctica?!

Have a great week!

Ange:)