In estimation theory and statistics, the Cramer-Rao lower bound (CRLB), named in honor of Harald Cramer and Calyampudi Rao who were among the first to derive it, expresses a lower bound on the variance of estimator of a deterministic parameter. The CRLB tells the best we can ever expect to be able to do (with an unbiased estimator).

The simultaneous localization and mapping (SLAM) problem asks if it is possible for a mobile robot to be placed at unknown location in an unknown environment and for the robot to incrementally build a consistent map of this environment while simultaneously determining its location within this map.