Which day of the week is considered the first day: is it Sunday or Monday?
This is a math issue, as we teach calendars, time-keeping, etc. in math class and curriculum. After beating around the bush for quite a while describing the context of the question, I am now ready to provide an answer.
It depends. It depends on you, your country, and your employer. Not very satisfactory, is it?
The ISO 8601 standard recommends that everyone adopt these points when discussing dates:
- The first day of the week is Monday
- The first week of the year is the week containing the first Thursday in the year
- Dates should be presented as YYYY-MM-DD
- Dates and times are shown as YYYY-MM-DDThh:mm:ss
- July 25, 2011 is today's date, written American style
- 25 July 2011 is how it would be written in the UK
Some decades ago I lived in the UK and received a new credit card from my bank in the US. The card said valid 5-8-90 which I believed was May 8, 1990. When I tried to use it in the UK, the merchants said it was not valid until 5 August 1990 and refused to accept it. I can confirm that this was a great nuisance.
After many years of confusion and completely scrambled up entries, the US Customs and Border Protection agency finally switched the blanks on its landing cards into the date format expected by foreign travelers (rather than expected by its US clerks). Notice that they did not use the ISO 8601 format! It's Day Month Year instead.
Imagine the confusion with applications, orders, flight reservations, etc. when people try to communicate across borders with the assumption that the people on the other side use the same time and date system!
So if we (in the US or EU or elsewhere) don't follow the recommended ISO method for writing dates, why would we (in the US) adopt the recommendation that Monday is the first day of the week?
Convention / tradition / habit often overrules a politician / mathematician / scientist / programmer's desire for order and efficiency.
PS - Did you notice the bullet point stating the first week is the week containing the first Thursday?
The weeks of the year system involves another recommendation that we Americans don't often use. Technically, it's called a "leap week calendar system." I will try to explain it tomorrow.