Errors in plate rotations as described by covariance matrices and their combination in reconstructions.

We use covariance matrices to describe the errors in plate rotations and to combine the contributions of individual plate pairs for plate reconstructions. First, for the rotation of a pair of plates the covariance matrix which describes the errors in the rotation is defined. Then we show how individual covariance matrices can be combined in a circuit of successive plate rotations to assess the errors in a plate reconstruction. -from Authors