Assuming you are referring to an ecothermometer, which is a device used to measure the temperature of the environment, there is no definitive answer to this question. It depends on what you are using the ecothermometer for and what temperature you are trying to measure. For example, if you are trying to measure the temperature of a room, the ideal eco temperature would be the temperature of the room itself. However, if you are trying to measure the temperature of a body of water, the ideal eco temperature would be the temperature of the surrounding air.