What unit should we use? Watts are way, way too big as there is no
floating/fixed point in sysfs. 10^-6 W is probably what is called for,
since we already need 10^-3 V and 10^-3 A. Small portable devices can
easily draw less than 10^-3 W nowadays.
"One disk to rule them all, One disk to find them. One disk to bring
them all and in the darkness grind them. In the Land of Redmond
where the shadows lie." -- The Silicon Valley Tarot