We compare the cost of borrowing an item to the cost of buying it new; a £110 drill borrowed for £10 is £100 saved.
We also count the carbon that would have gone into making another drill, because the greenest thing you own is the one you never had to buy.
It’s a small choice, but it saves you money and saves Exeter some carbon, and that adds up.
Where we’ve had to estimate, we say so – and we’ll improve the numbers as we collect more of our own data.