A field device for process instrumentation comprises a measuring and comparison device and a readable storage element. The measuring and comparison device is configured for monitoring an operating characteristic variable for compliance with a predefined range. The readable storage element maintains a state. The storage element state is permanently changed if a value held by the operating characteristic variable goes out of said predefined range. The predefined range is determined in such a manner that, as a result of a changed state of the storage element, a loss of suitability of the field device for special operation with an operating characteristic variable with restricted specifications, but not a loss of suitability for normal operation with an operating characteristic variable with less restricted specifications, is indicated.