# Collaborating quantities

Understand the physical quantities and how they work together and you can understand your bills and what to do to make savings.

The cast is limited: only 4 physical quantities.

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- power arrows, showing what you're demanding
- how long pies, showing the fraction of a slot for which you make that demand
- cost boxes, combining power and how long
- energy bars, showing what you pay for

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### For completeness

energy = power × duration

or

how many kilowatt-hours = how many kilowatts × how many hours