chooks chick gave you tons of great advice!!! I now have two, and let me just add that the new lg bators i have has eerything except the heating element enclosed! My temps hold steady within 1.5 degrees going from 85+ in the house to 72. they do really do a good job in regulating.
I also totally agree about getting it regulated for a whole day+ BEFORE you add eggs. This isnt just for temperature, but also for your humidity! I have found adding water through a syringe only throught he top window or run tubing in through a vent hole works wonders for consistancy also. do not make one adjustment after another.. You will get wild temperatures becaus eyou havent let your one adjustment run its course before the next. Thats why its always good to get it stabilised first.
The temp will drop when you first add eggs. mine went down to 85 right after i got my eggs in.. i also use 3+ thermometers and 1-2 hygrometers in each. use the law of averages!!! if one thermometers red bulb is near the element and the other one is in the middle and they only read 2 degrees from each other and the digital reads in the middle.. .. its a great temp.
I really really DO suggest rigging up your water like mine. its the most stable thing ive seen. in my experience adding water manually with the top off is just way to stressful and messy and pretty non- precise!!! If you would like a picture of it i have one ive posted before....
fishtank tubing( i got at a dollar store for 50 c) and the large syringe is sold at
tractor supply .. for 1.99 ( it doesnt come with a needle so no worries)
oh that thermometer in the window is $1 @
walmart. buy more than one and take note of their readings in the store. ones that read the same are more likely to be correct.
Edited to add: i also cut up brand new plain sponges into strips and put them into the water wells where my fishtank tubing is run to. When i need to refill, i just pull the syringe off the tubing, refill and reattach.