| Bit No. | Value | Meaning |
| 1 | 0 | Direction increments not given |
| 1 | Direction increments given | |
| 2 | 0 | Earth assumed spherical with radius 6367.47 km |
| 1 | Earth assumed oblate spheroidal with size as determined by IAU in 1965 (6378.160 km, 6356.775 km, f=1/297.0) | |
| 3-4 | Reserved | |
| 5 | 0 | Resolved u- and v-components of vector quantities relative to easterly and northerly directions |
| 1 | Resolved u- and v-components of vector quantities relative to the defined grid in the direction of increasing x and y (or i and j) coordinates respectively | |
| 6-8 | 0 | Reserved - set to zero |