At different locations on the earth, the variation will differ as will the rate of increase and/or decrease. Here's a graphic (on the left) that shows that. The actual values of variation have changed since this was put out, but it gives you an idea of the differences in variation.
![Photobucket](http://i120.photobucket.com/albums/o176/roccus45/Chapters20120to207_img_93.jpg)