None of these methods is foolproof. And none of them will work for all types of businesses. But try a few on your advertising efforts, and you'll get a sense of how well they're doing and whether the expenditure is giving you a satisfactory return on investment.
4. Revenue measurement: Lots of factors can impact your gross revenues, no matter what kind of business you run. But counting the till every day before, during and after an advertising campaign can tell you in absolute terms if you're doing something right. When you make your judgments on this, allow for mitigating factors (look at the last few years, for example, to see if there's normally a seasonality to your business).