Best way to verify temps in incubator

First off this is my first real attempt at hatching eggs. My first go round in a home made incubator had very inconsistant temps and I think cooked the eggs. Out of 9 eggs only two seem to have anything dark in them when candling. Anyways I got a used 'bater which brings me to my next question:

So I just piled 40 eggs into my LG still air incubator, and now I'm worried about temps. I have a wal-mart digital temp/humidity meter but after reading that these things can be "off" I'm worried. I also put a small cheap plastic "old school" type thermometer in there too but it's hard to see, do those things have to be upright? It is like a mercury thermometer but it has a red liquid in it with a small bulb on the bottom. Lastly I have a meat thermometer dropped down one of the air holes in the top just to see what it says.

I guess between the 3 I can hope to be close to the 100 degree mark, but I still don't feel confident. What would you do?