An alternative method and apparatus for determining a chemical injection dose to a fluid system is provided. The method and apparatus uses a monitor and control system processor connected to a pressure sensor and a positive displacement pump. The monitor and control system processor determines a stroke of a positive displacement pump by measuring a low-pressure on the suction side of the pump and equates each low pressure point with a pump stroke (or the discharge of a piston volume for dual stroke pumps). The monitor and control system processor calculates the dose by multiplying the number of low-pressure points with the volume of the discharge.