refractometer inconsistent

When taking my pre-boil gravity with my refractometer it's never consistent. For example last night I took 5 samples:

1st = 9.5 Brix
2nd = 10.5 Brix
3rd = 12 Brix
4th = 15 Brix
5th = 12 Brix

What gives? I ensure that the entire tip of the window is covered with wort when the flap is down.

Any help is appreciated.

Small hot samples will evaporate very quickly. I ran into this when I first got mine. Because the sample is so small, if even a small amount of evaporation occurs in the time it takes to put the sample on and lower the cover it can have a big affect (and variable too) on the reading.

It is better to take a bigger sample, let it cool, and then take a small bit to measure

You also need to make sure that their are no air bubbles in the sample or debris on the glass.

Ok, that I can do. I made sure to get rid of air bubbles and debris. But maybe Pjj2ba's ideas are my issue. Thanks!

I also found that the temperature of the refractometer itself can skew readings. I keep mine in the garage out of the sun in the summer and inside where its warm in the winter. I only get it right when I'm about to take a reading. I read somewhere that when they say Automatic Temp Correcting it means for the ambient temp of the device itself, not the sample on the glass. So if yours is an ATC model that is from 50-80F that means it needs to be in that temp range to get a correct reading. Here in Ohio we have about 3 days a year that fall within that range, the rest are higher or lower and I'm guessing that in Illinois you are about the same way

Yeah I read that too. And I also only get the refractometer out right when I'm to use it. I'll let you guys know sometime next week if I get it to read stable. I'll be brewing something.