Svara just mottaget från potens producent. Om någon skulle vara intresserad av "den magiska":
The scale with 2,5l just applies to the empty jug without funnel and cartridge. So the funnel with cartridge inside displaces the water in the jug. I just tried this out with my own Initium jug.
If you fill in 1000ml it´s the same amount of water, but it will be e little bit more at the scale.
I know, this is a little bit confusing, because the measurement can be read as the amount of filtered water. I´m very sorry for that. But I guess this explains the “magic” in this case.