Making the case for that payrise the hacker way

While reading http://news.ycombinator.com/item?id=1591225 about asking for a payrise, there was lots of talk of finding your market worth before asking.

This is the tool I use for that (Not mine, obviously). It gets source data from job adverts, so I assume that the upper bound might be inflated, and personal experience says that the lower bounds are typically shown as being higher than in practice. But the figures feel about right, and there is a lot of other nice bits of information too.