Inside in zone 30 flashed at 8 km/h too much without a trigger!

Hello guys, this morning I was really flashed in Zone 30 with exactly 38km/h (Blackbox GPS *in the car). Can anyone tell me if something like this is a bad joke? If it hadn’t been so cold I would have preferred to throw a stone into his box van. That’s something already harassment. Whom I pull off now still the 2 or 3km/h remain straight times 5km/h left which I drove too fast! At below 40km/h I can hardly get this myself as a driver from the speedometer u read without neglecting traffic. I assume that the cash registers are empty and flashed here to collect people even though they have still driven in the tolerance range! Has any of you already had such experiences?