To get those temp swings down to a minimum, make sure the stat is attached to something metal and within about 2-3 inches of the heat source.
To accomplish this, I used the metal housing from the comp fan and took off everything that wasnt needed, just left the fan and most of the metal housing.
If you use that and position it good, the housing will give you the optimal stat-attachment point and keep the new chicks away from the fan after they hatch.