Every month, football fans scratch their head at how teams can fall or rise in the World rankings despite losses, or periods of inactivity. In April 2016, the Republic of Ireland dropped two places to 31st despite beating the then 12th ranked side Switzerland, and drawing with the then ranked 26th team Slovakia.
Conversely north of the border a victory for Northern Ireland over 53rd ranked Slovenia, and a draw with the 17th ranked Wales meant that they jumped up two places.
When you look at it like that - it's hard to wonder how FIFA's rankings work.
Since the advent of FIFA rankings in 1992, the calculation system has undergone several major changes - until the most recent in 2006. The highly confusing results come about by looking more than just a result of a game - including match status (friendly or competitive), opponent strength, region strength, and results for the last FOUR YEARS.
This means that a look at the rankings this month show South American teams rising - thanks to their World Cup qualifiers, compared to European teams who played friendlies. It also means that teams like Northern Ireland whose rise has been very sudden - aren't losing big results in the last four years compared to Ireland.
Results are downgraded in importance for the rankings after every year - which means March 2013 results like beating Poland, or drawing with Sweden or Austria don't count anymore, or the Republic's draw with Poland last March doesn't seem as important.
What it does mean for the rankings is that Northern Ireland are at their highest ranking in their history in 26th, just two spots behind Wales. The Republic are in 31st, behind Czech Republic and USA, but ahead of Slovakia.
There's a new number 1 in the world - with Argentina claiming top spot ahead of Republic of Ireland's Euro 2016 rivals Belgium. Indeed, all of the Republic's opponents dropped in the rankings - with Italy moving down to 15th, and Sweden down to 36th.
The next time there will be any chance of a change in the rankings will be after May's friendly against the Netherlands. The Republic of Ireland haven't played a game in April in a few years, but there are a number of old May results - drawing with England in 2013, losing to Turkey in 2014 - that will affect's Ireland's ranking.
