The heating element in an electric oven is either "on" or "off". When the thermostat senses that the oven temperature is too low, it turns on the heating element and re-heats the oven. Electric ovens typically have a temperature swing to them due to this cycling on and off and don't maintain a constant temperature.
Commercial gas ovens have a "by-pass" feature that allows the flame to be set to low thus providing precise temperature control. No temperature swing with gas.