It appears to be one that will automatically switch and will show red when the tank the handle points to is empty. You will then flip the handle to the other tank so it reads that one. Your manual should explain the operation. If you don't have a manual you can check it this way: with both tanks at least partially full, open both tank valves and the indicator will show green. Now close the valve on the tank the handle is pointing to and turn on your stove. The indicator should move to red and you should begin drawing from the other tank. When you move the handle toward the open tank it should again show green.