How are you measuring power in your wearable?

Wearables are a low power design challenge, often powered by a single LiPo or coin cell.

I'd estimate the simpler devices, like fitness trackers, would consume a few nA up to around 20mA.

More complex devices running an OS are going to push from nA, or likely uA, up to hundreds of mA.

So... with dynamic ranges like that - how are you measuring your system power, and calculating battery life?

Oh, and crossed-fingers isn't a good answer ;-)