Have you ever wondered why you can sometimes have a perfectly audible conversation on a mobile phone when you only have one 'bar' of signal, while at other times, with five bars, your conversation keeps breaking up and crackling?

Dan's Data has an excellent post that explains: it's all down to signal-to-noise ratios. That's because the signal bars on your phone only measure signal - how well they can hear the local transmitter. They don't measure the noise, or how well the transmitter can hear your phone.

It turns out a corollary of this pertains to batteries, both for phones and for laptops. Your battery meter ends up having a logarithmic scale, effectively, because it can take a long time to drop from full to one notch down, but can move drastically downwards from there.