Abstract: An observation lock detector receives I and Q correlations and measurement residuals and transforms the I and Q quadrature correlation outputs based upon computed code phase and carrier phase into transformed I and Q quadrature signals communicated to conventional output lock detectors to provide validity and confidence indicator signals for indicating that the residual estimates are valid for dynamic propagation of the residuals in a navigation receiver for improved performance especially in low signal-to-noise environments such as for use in an ultratight GPS navigation system.