| 0, 0 (=E or BE) | Steady state or entrance to SC or BC (n or k =0) |
| A, E, T (=AE) | Outlet, entrance, total (i.e. from outlet to entrance) |
| B, S | Basic channel or sub-channel (=channel region) |
| A, S, F, D, X (P = A + S + F + D + X) and G | Acceleration, static head, direct and additional friction, external pressure differences (in connection with ΔP) and pressure differences due to changes in mass flux |
| Mn, BMk | Mean values over SC or BC nodes |
| Nn, Bk | SC or BC node boundaries (n = 0 or k = 0: Entrance) |
| D | Drift |
| S, W | Steam, water |
| P, T | Derivative at constant pressure or temperature |
| TW | Tube wall surface |