You enter the estimated number of gallons per day that the tank uses. The computer then automatically determines when to deliver next.
Example: Let's assume you have a water heater hooked to a 50 gallon tank that uses about one gallon of propane per day. If you fill the tank on January 1st, in 42 days it will be out of fuel (50 gallons X 85 percent of the maximum filling capacity of the tank). The computer knows that you want to return when the tank reaches a certain minimum level (let's say that you've decided that's 20 percent). It will schedule the next delivery for February 2nd which is 32 days after the last delivery. By that time, the the customer will have used approximately 32 gallons leaving about 10 gallons in the tank (20 percent).
In this example you would enter a "1" to reflect the 1 gallon per day usage rate for the water heater, like this:
Be sure to also enter the as this is also used in calculating a new return date.