A method and device are provided for measuring and/or adjusting the cleaning performance of a cleaning liquid. One method of the invention includes determining a control value (i.e., the number of drops of the cleaning liquid to provide a selected volume) indicative of when the cleaning performance of the cleaning liquid is at or approaching an unacceptable level. At least one substrate can be contacted with the cleaning liquid and a drop number for the cleaning liquid (i.e., the number of drops of the cleaning liquid to provide the selected volume) again measured. At least one cleaning agent, such as at least one surfactant, can be added to the cleaning liquid when the measured drop number is at or near the control value. In one embodiment, the cleaning agent can be added until the measured drop number is at or near a baseline drop number for the cleaning liquid (i.e., the number of drops of the cleaning liquid when cleaning performance is acceptable).