Broken Hydrometer?

Might answer my own question here but can a hydrometer just be defective out of the box? I check between 70-80 degrees figuring it might read 2 points low on that higher end. I always take my measurement when I have the full amount of water mixed in. This hydrometer consistently tells me I'm missing OG consistently around 50-60% efficiency. So I've always been bumping up extra DME to equal out a brew. And I consistently get beers that taste stronger than I expected. Two weeks ago it said I missed target OG by .010 points on an extract brew. Tonight I was horrified when it said I missed my first AG brew by .020 points. So as usual I mixed in some DME to bump up my gravity. Could this thing have been bung out of the box? Is there a way to calibrate/test it? They're cheap enough, I should just pick up another. Dropped a couple hundy to go AG, it was fun and I was meticulous with watching videos and following instructions. Milled the grains, mashed for 45 min sparged for 30 min. Hope I don't just suck at it.

Easy calibration: pop it into a tall glass of room-temperature water and the reading should come out to 1.000 exactly. Anything over or under that means a defective unit.

Hydrometers are calibrated at 60* and give a true read at that temp. Use water at 60* and see if you get a correct reading .999; if not at .999 at 60* adjust for the difference. It sounds like you are missing something in the mash. Stir the heck out of it at dough in, hit the mash temp. for specified time or convertion, sparge water to raise grist temp. to 165- 170* stir in real good and drain. Check your crush! That is the first place to start. The problem is in your equipment or process, and the hydrometer is telling you just that. Nothing that can not be corrected. More details are needed; grain bill, ect. cheers

You can use the table found here to adjust the reading based on the temperature

http://howtobrew.com/appendices/appendixA.html

It should be 60°F in distilled water. YMMV with just tap water.

Phew. Felling a little better. Distilled water at 60 degrees read 0.992 below the meniscus which this hydrometer calls for. So my extract brew was spot on and I only missed my AG by a couple points. Hey, 60% efficiency on your first try is more rewarding than the 30% or so I thought I did. I used a 2 liter soda bottle for the hydro test and it kept wanting to turn a little sideways in the bottle so I worried that my table wasn’t level, so after I pulled out my level to see I figured it was just the instrument being funny. I got it to be strait and still long enough to get a reading. Anyway, doesn’t matter, I’ll just get a new one.