Is my hydrometer broken??

[spbrhs07]

So it's been about 4 months since I last brewed and decided I'd waited long enough. Last Tuesday I threw together a partial mash saison and pitched one of my favorite Wyeast strains of Belgian yeast from a 2L starter. It was a 5 gallon batch and when I added the yeast, the bucket had already been topped off to 5 gallons so I ended up with closer to 5.5 gallons in the bucket. Who cares?! I stirred it all together and aerated well and then took my OG reading. 1.052 - right on target! Now here I am 6 days later and ready to keg and I find the gravity to be about 1.030?!?! WTF!! What the hell I decided to taste it and see if it is at least drinkable... It tastes flawless! As I have made this recipe numerous times in the past, it tastes exactly as it should at it's target FG of 1.012. Anyways I kegged it and I'm drinking it anyways... but I want answers! The only explanation I can come with is a faulty hydrometer.. is that even possible? What else could be going on here?

 

[Gnomebrewer]

Check your hydrometer in water (should read 1.000) then in a chilled (room temp) solution made up with 4oz sugar in 1/2 a quart of water (should read 1.092).

 

[TomVA]

Is that 4 oz of sugar by weight or volume? And is it corn sugar (glucose) or table sugar (sucrose)?

TomVA