I mean, I want the meter to calculate how much water is flowing through per min - basically we have a system that needs water to flow through at a rate of 4 L/MIN or more and I want this flow switch to tell me how much water is flowing through per/min
60/7.5 =8, for whatever that's worth. I'm not sure why you've got your brain tied in a knot over this.
1) Determine your frequency. There are many ways to do this; e.g., count the number of pulses occuring in 10 seconds and divide by 10, that's your frequency in Hz.
2) Divide the frequency by 7.5 and that's your flow rate in L/min.
If you do as in the example on the referenced page tell you, you will measure the number of 2.25 ml pulses for 1 second.
444 pulses measured in 1 second equals 1l/s. If you divide this number with 7.4 The result will be 60, and this is equal to 60 l/min.
Just for the record, the number 7.5 is derived from using 2.2 ml as a measure for each pulse. 7.4 is correct if you use 2.25 ml/pulse. You get to this number by dividing (1000ml/2.25ml/pulse/s)/60s=444/60=7.4