This is an idea spun out of conversation with Ben and Paul at last night’s LRUG – a physical device for alerting developers working in a continuous build environment as to how far they are from the trunk.

Because of the rate of change on an agile project, it’s important to keep your own personal codebase as close to the trunk as possible, otherwise you’ll spend a long while working on code that doesn’t fit with the current state of the system, or working around issues which may have been fixed. It’d be good to have some sort of physical display to alert you to this, rather than relying on typing svn up every five minutes.

Enter the continuous build barometer. It’s dead simple: it’s a dial you connect to your computer via a USB connection. The moment you do a checkout, the needle sets itself to 0. And then, as your codebase diverges from the trunk, the needle indicates how far (proportionally) your code diversifies from the original. And, of course, the moment you check in, the needle resets itself to zero.

Ideally, the continuous-build barometer needs to be made out of something reasonably heavy – I have this image of brass and wood, much like this example, if only to convey the weight that “checking in often” actually carries. In terms of making one… dial indicators seem to be quite pricey. It’d be easy to prototype with something like this ten-bar LED display, an Arduino board, and a short-ish script to compare the trunk with your local version, cronned to run regularly. Of course, I think the physical nature of the object is important, but it’d still be interesting to see what a working version in any form looked like.

That was one of my favourite things this month’s LRUG gave me, and it’s not really even code. Now: who wants one?