Sm Hydra issues

[jonumberone]

My Hydra does the same thing. I placed all my hydros on the shelf with it and all read about 8 points lower than the hydra.
I had it replaced by them and the new one does the same thing. I just set the hydra for 73% and all my hydros read 64 -65 on every shelf.
I also found the hydra reads 10 to 11 % higher for the first few days after I fill it, then it comes back down to the 8% difference.