How to choose a ballast

The resistance increases as the ballast heats up, it is ni-chrome wire. Properly sized for wattage, it should not get hot as in a heating element. Most often resistance measurements are done at 25C, or near room temperature.

Measurements can be done with an Ohmmeter, but only the more expensive ones do an accurate job at low Ohms. Hooking a ballast and coil in series, and measuring the voltage drops for near 50% is a good ball park test.