:<math>\mbox{TVD} = (180/\pi)\sum (\mbox{MD}_{i} - \mbox{MD}_{i-1}) \times (\sin \alpha_{i} - \sin \alpha_{i-1}) /(\alpha_{i} - \alpha_{i-1})</math> | :<math>\mbox{TVD} = (180/\pi)\sum (\mbox{MD}_{i} - \mbox{MD}_{i-1}) \times (\sin \alpha_{i} - \sin \alpha_{i-1}) /(\alpha_{i} - \alpha_{i-1})</math> |