Thanx for help so far. I ll try to concentrate to the read code, no need to remove the other code, it works with other sensor brand. I think the loop is wrong. in order to test the while loop needs to read till 0xFF, so it adds one more read.
I am not sure what serial1.flush does there, since it seems to work as an OUT statement, I don’t get it.
I think I ll just scan for 0xFF, then read next 3 bytes and just go for evaluation. I am not a programmer but I manage in the end 
It was great help you saw that actually checksum adds, somehow I thought it way off (without calculating… )