It is shown that the covariance matrix of object location errors is identical for time of arrival (TOA) and time difference of arrival (TDOA) systems if the inverse of the covariance matrix of TOA (TDOA) errors is used as a weighting matrix. Also, with this weighting the location errors statistics do not depend on the particular difference pairs in the TDOA scheme, provided that a complete and nonredundant set is used. If the TOA or TDOA errors are samples of jointly Gaussian random variables, this weighting is optimal in the sense of maximum likelikhood and minimum variance. Only relative values of the weighting need be known for optimality.