A method for dynamically determining the volume of a liquid dispensed by a
metering system, the metering system including a metering pump, a pump
motor, a sensor, and a conduit interconnecting the pump and a metering
probe. The method includes the steps of aspirating a quantity of fluid
into the metering probe using the metering pump, moving the probe
relative to a reaction vessel, and dispensing the fluid. The dispensing
step includes the steps of identifying an onset point associated with a
parameter which can be measured by the metering system, identifying an
end point associated with the measurable parameter, and timing the pump
motor during the period between the onset point and the end point in
order to determine fluid volume. The sensor, such as a pressure
transducer or capacitance change sensor, disposed in relation to the
conduit can detect changes in the parameter and identify the onset and
end points.