Original Gravity Changed? ?

[Tizzomes]

So I brewed a all grain pale ale on Fri and had a gravity question. After chilling the beer I poured a bit into a glass to take a reading. I got an O.G of 1.040 I was off by 10! So the next day just out if curiosity I took another reading from the glass I never cleaned out. I got a reading of 1.056 by the way I'm using a refractometer.Would the following day reading be the one to go by??

 

[sudsmcgee]

It probably evaporated.

 

[Tizzomes]

It probably evaporated.

Good point, the original O.G reading was done around 78 degrees.
But you think I was still off uh?