How much coffee do you drink? add it up, compare it to how much you actually pay for public education.

FORBES: Connect

Some, for example, will add the two mortgages together and then compare that total borrowing to your income and expenditure.

BBC: Fergus Muirhead

Which means that we have to find some similar measure of value add in a company, not turnover, which we can compare with GDP.

FORBES: Occupy London: Falling at the First Step for GDP != Turnover

It's impossible to add up all the indirect environmental costs of a windmill, but a good proxy for this arithmetic is simply to compare the resources consumed (in dollars) with the output produced (in dollar value of the electricity).

FORBES: Environmentalist, Spare That Tree