threshold trigger VS up/down counter

I need to measure the a (high) frequency input (on I4) transmitted by a (24V) flow meter in a water circuit.
The flowmeter has a paddlewheel and -in my case- give a frequency between 0 and 100Hz.

In order to display the flow, i tried both a threshold trigger and an up/down counter.

When testing with a manual set Input, I found that the threshold trigger outputs the frequency as put in the Input, but the Up/Down counter gives always lower number.

The difference exceeds 10% for lower frequencies but reduces on higher frequencies.

The difference is so high, i can only assume my flow chart is wrong.

Any idea?

Yes thanks a lot you are right. No difference with an 'live' input.

regards,

JOhan