electricity meter gadtet

[brainybox123]

I read somewhere about a gadget that you can have on show which shows how much electricity you are using, for example when the TV goes on, you can see visually how fast the thing is turning and, again, when you switch, say, a light off, you can see it slow down. A great way to know how much electricity each thing takes in comparison to each other.

Does anyone know what it's called please?! Think it began with O but not entirely sure.

Thanks