This is a small subset of qx (actually the bits 7+6 of qx).
qc can have 1 of the following numeric values:
- 0 : BAD - The dp value is not useful
- 1 : UNCERTAIN - The quality of the dp value is less than normal but the value may still be useful
- 2 : GOOD (non-cascade) - The quality of the dp value is good
- 3 : GOOD (cascade) - The quality of the dp value is good and may be used in control