To calculate the change in temperature, subtract the initial temperature from the final temperature. Example: 84.2 degree Fahrenheit - 41 degrees Fahrenheit = 43.2 degrees Fahrenheit. The temperature from morning to afternoon changed by 43.2 degrees Fahrenheit.
It needs 12 volts so it will be the standard modern power supply provides 12 volts of power.
Modern coil designs produce voltage pulses up in the neighborhood of 40,000 volts from the interruption of the 12 volt power supplied by the battery. Some modern engines have multiple ignition coils mounted directly on the sparkplugs.