It's not really a data logger. it tells you at what time and what % it was stopped when the cycle was broken the first time.
You have to reset it each time, it does not over right. So if you didn't reset it prior to that run, it still has the information from some previous run.
To see the data, you go to the initial screen...where it says "Edelbrock Nitrous Systems....then the voltage" and hold down the Enter button. The first number is the time that the cycle was interupted the second is the % it was interupted.
To reset it, continue holding it until it says "release" release the button and it will say "Erased" and your ready to go.