word. Bits 30 to 31 are the Sign/Status Matrix (SSM) - these bits may have various encodings dependent on the particular data representation applied to a given word: In all cases using the SSM, these bits may be encoded to indicate: Normal Operation (NO) - Indicates the data in this word is considered to be correct data. Functional Test (FT) - Indicates that the data is being provided by a test source. Failure Warning (FW) - Indicates a failure which causes the data to be suspect or missing. No Computed Data (NCD) - Indicates that the data is missing or inaccurate for some reason other than a failure. For example, autopilot commands will show as NCD when the autopilot is not turned on. In the case of Binary Coded Decimal (BCD) representation, the SSM may also indicate the Sign (+/-) of the data or some information analogous to sign, like an orientation (North/South; East/West). When so indicating sign, the SSM is also considered to be indicating Normal Operation. In the case of two's-complement representation of signed binary numbers (BNR), Bit 29 represents the number's sign; that is, sign indication is delegated to Bit 29 in this case. In the case of discrete data representation (e.g., bit-fields), the SSM has a different, signless encoding. {| class="wikitable" border="1" |- ! colspan="2" align="center" | SSM ! colspan="3" align="center" | Data Dependent SSM Encodings: |- ! align="left" | Bit 31 ! Bit 30 ! Sign/Status Matrix for BCD Data ! Status Matrix for BNR Data ! Status Matrix for Discrete Data |- | align="center" | 0 | align="center" | 0 | Plus, North, East, Right, To, Above | Failure Warning (FW) | Verified Data, Normal Operation |- | align="center" | 0 | align="center" | 1 | No Computed Data (NCD) | No Computed Data (NCD) | No Computed Data (NCD) |- | align="center" | 1 | align="center" | 0 | Functional Test (FT) | Functional Test (FT) | Functional Test (FT) |- | align="center" | 1 | align="center" | 1 | Minus, South, West, Left, From, Below | Normal Operation (NO) | Failure Warning (FW) |- |} {| class="wikitable" border="1" |- ! Bit 29 ! Sign Matrix for BNR Data |- | align="center" | 0 | Plus, North, East, Right, To, Above |- | align="center" | 1 | Minus, South, West, Left, From, Below |} Bits 11 to 29 contain the data. Bit-field discrete