freQuensy

Where?

I am playing KSP v 1.8. and I want to calculate the time that the rocket stage will operate. So I use definition of ISP: As we can see, the error is exactly 10 times. The same error persists when flying with other engines (for example 24-77). I cannot understand that something is wrong in my formulas, or does the game somehow determine the specific impulse and thrust of the drive? What's the problem here? Surely someone asked the same question.