This topic is about electric connection, signal curves and interfaces.

Flow consumption signal from Direct P, Direct PN and Delta PN is just usual pulses. You need to count pulses right. Weight of pulse (in milliliters) is shown in device passport.
For Eurosens Direct P - each flow meter has own weight of pulse, according to manufacturer's benchmart  after assembly.

For Eurosens Direct PN and Delta PN it is constant:
for 100 serie - 0.005 liter
for 250 serie - 0.01 liter
for 500 serie - 0.02 liter

Some cheap GPS trackers can't perform with flow meters it well because don't have internal timer and rely only for GPS receiver for time information. That means that if no GPS signal - pulses can be not registered and measurement will be wrong.