Class 4 (Extended Register) couples measurement values with a status byte and capture timestamp.

Standard Status Bitmask (DLMS Blue Book Ed. 14)

Bit 0: Invalid Data (Value calculation corrupted or sensor offline)
Bit 1: Doubtful Value (Uncertain measurement precision)
Bit 2: Measurement Value Modified (Manual adjustment or calibration)
Bit 3: Power Failure (Occurred during integration period)
Bit 4: Clock Synchronized (RTC synchronized via external time server)
Bit 5: Daylight Saving Time Active
Bit 6: Overflow (Energy register counter rollover)
Bit 7: Reverse Energy Flow Detected (Indicates possible reverse wiring/tamper)

Checking Bit 7 on Active Energy Import registers immediately detects field wiring inversion errors!