Abstract: A meter for a machine employing a fluid fuel, and receiving fuel in proportion to machine demand, for indicating output of the machine in relation to fuel consumption, e.g. miles per gallon. A gas can be injected into the fuel line, in dependence on machine output, e.g. miles traversed, for formation of gas bubbles therein and slug flow of fuel through a length of the fuel line. Bubble sensing and signal output means are provided for sensing bubbles in the length of the line, and producing an output signal which is a measure of the machine output in relation to fuel consumption. An indicator is operatively connected to the bubble sensing and signal output means and indicates the machine output in relation to fuel consumption. Instead of gas bubbles, another signal, which is a measure of machine output can be employed.