Hi there.
Like Junebuggena said; you'll need to get a humidity probe asap.
Humidity is measured by surface area and not the volume of water.
* If your humidity is too low you run the risk of your eggs drying out (this is a common issue when incubating button quail), as well as hatching difficulty due to the membrane not being properly saturated.
* If your humidity is to high, the eggs won't be able to develop at a normal rate. This could cause a late hatch or the chicks simply wither away without you being aware.
Humidity, is a very important aspect of incubation. There is room for reasonable fluctuation, unlike the temperate requirement, but it's best to keep the incubator running at the prescribed optimal set values for incubation.
Hope it helps.
ABOT