TextMate Math Bundle and the Box Model
I love TextMate, oh yes I do. One thing I’ve found incredibly useful lately is the Math Bundle, which you can install yourself by pasting the script listed here into a Terminal window.
So, you know how in the CSS box model padding is NOT regarded as part of the width of the box, and you always have to rack your brain to subtract out the padding from the marquee you’ve measured in your graphics app? Well, not any more!
The Math bundle, among other things, lets you evaluate arithmetic expressions in your text documents. So let’s say I’ve got a div (#column_1) that has horizontal padding of 26 pixels, but a total width of 228 pixels as in the image below:

All those CSS experts out there know that I really need the width set to 228 – 26*2 pixels to take the padding into account, so let’s type that out:

Now, before I grab that sheet of paper and/or caffeine to do the sums, I just highlight the expression, press Shift-Ctrl-C and I get this:

Now I hit 2 to replace the expression (since my browser surely won’t understand my advanced mathematics), and voila! Instant box-model love:

Like I said, you gotta love TextMate! Makes me wonder why I even bothered studying maths up to a university level…