i would like to understand better this forumla not to make further mistakes with other calculations
Calc = (NbTopsFan * 60 / 5.5); <<<<<<<<< THIS is the formula
pulses per second * 60 = pulses per minute. Divide by pulses per litre to get litres per minute.
NbTopsFan is number of turns arduino detects in determined time if i make delay of interrupt of 1 second it will calculate turns douring 1 second
No. NbTopsFan is the number of pulses. - the "Pulse frequency" as clearly stated.
The 5.5 is the calibration (pulse/litre)
60 is minute? 1 hour
Either, neither, or both. You asked for pulses per litre. The time is irrelevant. I think you should ignore this anyway. It doesn't match with the formula. I don't think the seed crowd know what they are doing. I have already posted Oxer's programme, he does know what he is doing, and properly explains it.