I was checked my SG/OG and it was WAY off. So I knew everything was right so I just said, "Oh well" and sealed up the fermentor. Then I mixed the 2nd batch and got an even lower reading. Like 1.060 when it should have been upwards of 1.080. I had another hydrometer so I used that one and low and behold, that one read 1.084! The first one was a full .024 off! Un real!
So always have a spare! Hydro #1 is now in the trash.
BTW: This was for wine, not beer. But I have used this one for beer from time to time like every 10th batch and always thought it came out low.