Comass ($\Vert {\phi }_x{\Vert }_{\ast }={\sup }_{\xi \text{ oriented unit simple }p\text{-vector}}|{\phi }_x(\xi )|$)

The comass is the operator norm of a differential form restricted to simple unit tangent multivectors. Reversing orientation gives the equivalent two-sided bound. It differs from the Euclidean norm of all the form's components. The calibration bound uses comass because tangent planes are represented by simple multivectors.