In my day job, I am an embedded C programmer. Our devices work with flow measurement and use a bunch of floating point math for accumulators and such. In the past three years, I have learned some interesting things about floating point numbers and how they cannot represent certain values. I was therefore amused to see an easy example of the floating point problem when I was paying for postage last night:

I wonder how much it deducted from my PayPal account . . .