Steam power is represented in two ways, both requiring algebraic equations. These can be measured and graphed by non-revenue cars (usually converted from retired passenger cars) equipped with dynamometers and drawbar sensors which respond to the locomotive's pull.

• Tractive effort—more accurate. The force exerted at the rim of the driving wheel, measured as vertical lift. This depends on driver diameter, cylinder diameter, piston stroke length, and boiler (steam) pressure. This is very accurate but must be converted to train loads and pulling capacity.
• Drawbar horsepower—easier to measure. A time factor of feet/pounds (horsepower) multiplied by energy in Joules or Watts, this depends on fuel quality and burning rate, boiler diameter and evaporation rate (steam production), cylinder efficiency, and—believe it or not, the strength and efficiency of the fireman.