@tbowmo Good hint. But it is happening to all three sensbeners for at least one month now. (different orders). I now got 4 more so I will test again soon.

Over xmas I tested also with magnesium chloride hexahydrate. magnesium chloride hexahydrate produces exactly 33%rel.

All 3 sensbenders report exactly 39% or 40%. So they are also here 7% off. But almost the same value and very reproducible - so thats great!