Abstract: A system and method for measuring the operation of a device is disclosed. A plurality of virtual sensors which define a multi-dimensional virtual sensor space sense the operation of the device. A normal operation determiner determines at least one region of normal operation for the device. An abnormal condition determiner provides a warning when the operation does not fall within the normal operation region which is defined within the multi-dimensional virtual sensor space. A maintenance method and system are also disclosed for maintaining at least one device. The maintenance system includes a measurement system and an abnormality processor. The measurement system measures the operation of the device and provides an indication of when the device is not operating normally. The abnormality processor predicts, based on the output of the measurement system, when the device is likely to fail.