The pressure-time method is used to determine the flow rate in hydraulic turbines. Over the years, developments of the method to improve its accuracy have been proposed, such as a time dependent friction (Jonsson) or a different upper integration limit (Adamkowski). The present work investigates these developments on measurements performed on a full-scale machine for different flow rates. The discharge computed values using pressure measurements are compared to ultrasound transit time measurements performed simultaneously. The results point out the significance of the developments on the final results; variations of 0.5% are obtained when combining Jonsson friction formulation and Adamkowski upper integration limit.