On the DeveloperTutorials website, there's a new tutorial posted that warns against the perils of floating point comparisons between PHP and Javascript.

The problem is if you've done any calculations to arrive at these numbers they might actually be stored as 71.00000000001. Now if one of them is stored that way and the other isn't and you compare the two to see if they are equal you'll get a FALSE as the response, even though they should be the same. This isn't a bug, it's how floating point comparisons are designed to work.

In order to help combat this, he's provided two functions - one in PHP and one in Javascript - that compare the numbers in a more "sane" way that someone using them to store, say, currency values might want to use to compare them.