A fluid-working machine has working chambers, each of which is connected to a fluid commutating means which alternately connects the working chamber to either of two fluid manifolds. The first set of data comprises at least one of sensor data, motion data, and location data, and is real-time output from the inertial navigational device. The messages and electronic contracts being communicated between the association web site and each of the feet are encrypted and decrypted by using keys and digital signatures so as to protect from fraudulent bid by real association feet.