A liquid jet head includes a passage-forming substrate composed of a crystal substrate provided with pressure-generating chambers communicating with nozzle orifices and piezoelectric elements disposed on the passage-forming substrate and each composed of a lower electrode, a piezoelectric material layer, and an upper electrode to cause a change of pressure in the pressure-generating chamber. The method includes providing a diagnostic monitor, the diagnostic monitor being configured to be capable of executing even if the OS kernel fails to execute, the diagnostic monitor having a monitor trap arrangement. Each base-array index is thereby at least implicitly associated with a cumulative base value equal to the sum of all preceding base indexes’ associated subarray sizes.