TheStreet's Jim Cramer says Fitbit's (FIT) products may be the 'greatest thing since sliced bread,' but the company's CEO James Park needs to do a better job of managing the company. Cramer spoke with the health and wellness device company's ceo on Squawk on The Street and said, 'sometimes you have to take a CEO and put his feet to the fire.' Park reiterated that Fitbit is building a health and wellness company that is rolling into China and makes devices that people want, but Cramer said Park needs to 'play by the rules.' And, the rules in this case mean 'the rule of numbers.' Cramer said, 'In the end, we’re bound by the four boundries of the spreadsheets. We’d like not to be. We’d like to be big thinkers. It’s true that Netflix (NFLX) and Amazon (AMZN) are the two companies in my life that have not been controlled by the spreadsheets. But the spreadsheet here doesn’t add up.'