I believe I have found a mistake in the code!!
It says
Calc = (NbTopsFan * 60 / 7.5); to give the litres per minute.
This line is incorrect as NbTopsFan gives the amount of pulses in the one minute time.
60 is the amount of seconds in a minute
and 7.5 is the litre converter
so at the moment, using units only, the result is min/L
so just change it around to get an appropriate result
Calc = (NbTopsFan * 7.5 / 60) // this will result in pulses(litres)/minute
hey presto all you people wondering why your code didn’t work 