Measurement and use of hydraulic stiffness properties of hydraulic apparatus

A method of determining one or more properties of a hydraulic apparatus, the apparatus comprising:

• a hydraulic machine and a hydraulic circuit region in hydraulic communication with the hydraulic machine, the hydraulic machine being controllable to displace pulses of hydraulic fluid of one of a plurality of different volumes into or out of the hydraulic circuit region, the method comprising:
• determining a pulse parameter corresponding to a required volume of hydraulic fluid to displace in one or more pulses;
• controlling the hydraulic machine to displace one or more pulses of hydraulic fluid of the required volume into or out of the hydraulic circuit region in dependence on the pulse parameter;
• making at least one measurement of the response of part of the hydraulic apparatus to the said one or more pulses;
• and
• determining the one or more properties of the hydraulic apparatus in dependence on the measured response and the pulse parameter.