Add a Bulb Thermometer.
Make a cardboard pocket for the bulb thermometer. It can be just one layer
of cardboard with a slot for the thermometer with a second layer for a cover.
The whole assembly can be glued over a hole on the back of the incubator.
When your thermometer has been installed, compare its reading with the reading
of the thermistor. Take data every 15 seconds over several cycle. Record
the time, thermometer reading, thermistor reading, and whether the bulb
is on or off. You will probably want to graph your data for a report.