Roughly Pi Day

I am getting my grump in early so I can batten down the hatches, pull my scarf up around my neck and grit my teeth when everyone else gets very excited around the middle of March about ‘Pi Day’.  For anyone who is new to this, ‘Pi Day’ is celebrated on 14^th March, written in England as 14/3, or 14.3.13 or 14/3/13 if you want to include the year too.

In the USA the month and day are transposed, so it would be 3.14.13, which looks rather bizarre to me, although it is only ambiguous when the day of the month is 12 or below.  Is 4/5/13 the fourth of May (UK) or the fifth of April (USA)?  Incidentally, in the UK we use 9/11 to refer to the attacks because the name comes from the USA.  The London terrorist bombings in the summer of 2006 are referred to as 7/7, but this is the same in both systems.

[As it happens both systems are unhelpful.  It would seem to make far more sense to put the year, followed by the month and then the day, not least because when these are sorted numerically they appear in order.  Today would therefore be 20130303 which comes before 20130304, etc.  This is the way I label computer files that need dates.  xkcd agrees with me.]

 14^th March, in the US system, is 3.14, which is the start of the decimal approximation of pi, 3.1415926 … etc.  So this gets used as Pi Day. 

I have no problem with a day where everyone talks lots about pi and how extraordinary and interesting pi is.  There are lots of exciting things to talk about at different levels, and the idea of a shared mathematical experience across different classes in school is a good one.

So what’s the problem?   Pi is not 3.14

I would much prefer “Pi approximation day”.  But that has already been taken for 22/7 (in the UK system), because the fraction 22/7 is a commonly used approximation for pi. 

Now, I am not sure that 22/7 is used much nowadays because calculators are ubiquitous, so there isn’t much need (I am sure I can recall old exam papers that had circles with radius a multiple of 7 to make the pre-calculator calculations easier).  But the particularly strange thing here is that 22/7 is actually a better approximation (in the sense of having a smaller error) than 3.14 is!  [But  22^nd July is often not during school term time, so it isn’t a helpful maths day anyway.]

I will swim against the tide and refer to 14^th March as “Roughly Pi day” and an activity I will do with pupils is to look at the percentage errors in different approximations to pi, from 22/7 to 3.14 to 333/106 to 355/113.

A final thought: the day following the 14^th is the Ides of March.  Down with dictators and those who fail to make it clear they have rounded pi!