If there is one question to rule all of marketing, it goes something like this: "On a scale of zero to 10, with 10 being the highest, how likely are you to recommend our company to a friend or colleague?"

That's how you get to the Net Promoter Score, which is how many companies determine overall customer satisfaction.

It's a simple question, but deriving the score isn't quite as simple. For example, if you asked 100 customers and 80 of them gave scores of nine or 10, that doesn't mean your NPS score is 80%.

You also have to subtract the detractors—those who gave a score of six or lower.