Automatic delivery is the preferred method of delivery for more than 90% of home heating oil customers. Automatic deliveries are scheduled through the office automatically using advanced computer software based on the degree day system. Degree days are a unit of cold or heat measured by the national weather service. The computer averages historical usage with current season usage to determine how many degree days equal 1 gallon of usage for your home. From there deliveries are scheduled with an optimum delivery of 180 gallons for a standard 275 gallon tank, or when your tank gauge is @ approximately ¼ of a tank. Because this system relies heavily on current usage it is important for customers who supplement their heat with other sources (i.e. wood, pellets) to monitor their tank levels when they stop supplementing their oil heat.