Formulas, worked examples and checklists. Every number is a labelled assumption.
How to add up purchase price, running costs and expected lifespan into a cost-per-year figure, with a worked example where the cheaper product loses.
A simple formula for turning an appliance wattage and daily usage into a monthly electricity cost, with worked examples and caveats about tiered rates.
What standby (vampire) power is, how to convert it into a monthly cost with a worked example, and practical ways to reduce it.
How to convert filter price and capacity into cost per gallon and per year, with a worked example comparing two kinds of filtration.