[conspire] check out AC power (Watt)meter (What's Your Watt?/...) from library

[Nick Moffitt]

Michael Paoli:
> One can check out AC power Wattmeter (What's Your Watt?) from
> library.

These devices are really useful for installations where you have a lot
of devices running.  You can accurately measure median loads, sample and
get a rolling average, and take note of peak load (typically on startup
for devices that have spinning rust).  

It's also amazing to look at two identical pieces of hardware and notice
that they have dramatically different power loads. Often you can trace
that to software load differences, and make adjustments as necessary.

But of course the best reason is for energy savings and capacity
planning.  You can work out that your mains bus can handle N servers at
normal load, and N/4 at peak load, or what have you.  Then you know to
only start up a quarter of your systems at any one time, and stagger
boots (or just increase capacity to cover full synchronised peak load).