This paper analyzes the pressure-time method and its developments. The pressure-time method used to determine the discharge in hydraulic turbines is described and applied in a generic test case in well controlled laboratory conditions. Developments of the method are presented: a time dependent friction factor (proposed by Jonsson) and a different upper integration limit (proposed by Adamkowski). Laboratory experiments are used to compute the discharge using the pressure-time method in the standard and modified versions and the results are compared. The precision of the methods is verified by comparing the computed discharge values to the values measured with a magnetic flowmeter.