We introduce <(0) over dot>, a new invariant time derivative with respect to a moving surface that is a modification of the classical delta/delta-derivative. The new operator offers significant advantages over its predecessor. In particular, it produces zero when applied to the surface metric tensors S-alpha beta and S-alpha beta and therefore permits free juggling of surface indices in the calculus of moving surfaces identities. As a result, the table of essential differential relationships is cut in half. To illustrate the utility of the operator, we present a calculus of moving surfaces proof of the Gauss-Bonnet theorem for smooth closed two dimensional hypersurfaces.