The bicycle barometer takes data about the weather, the status of the tube lines I use to get to work, and whether my local station is open or shut.
It then reduces all that data down to a single value and displays it on a dial with a bike sign at one end and a tube sign at the other.
For example, if it is raining a bit the dial will move a bit towards the tube sign, but if the tube is suffering delays, it will move a bit back in the other direction.
Different data points get different weightings. E.g. snow is more important than a bit of drizzle; the tube station being shut trumps everything.
The code, instructions and design for building one are available here: https://github.com/memespring/bicycle-barometer