Indeed, if you look the rain accumulation map for the next 24h, the picker indicates 7.9mm of rain. If you do the calculation with the meteogram also visible on the map, this is pretty much the same. Perfect.

Now the issue comes wihen you select the next 12h. As it is 5.00PM, I expect to see the rain accumulation for the next 12h finishing at 5.00AM which in theory, according to the meteogram, should cover all the rain so 7.9mm as well but as you can see on the other screen shot, the picker indicates only 3.5mm.

Why not 7.9mm ? Does that mean that it is not really the "next 12h" or the "next 24h" but the starting point is earlier, explaining then that the system doesn't take into account part of the rain during the night ? If it is the case how do you know when it starts to calculate the next 12h or the next 24h