Abstract: Some embodiments of the invention relate to methods carried out by an NSS receiver and/or a processing entity capable of receiving data therefrom, for estimating parameters derived from NSS signals useful to determine a position, and for estimating an expected accuracy. The method comprises receiving input data comprising NSS signals observed by the NSS receiver and/or information derived from said NSS signals; operating an estimation process, hereinafter referred to as “estimator”, using state variables and computing the values of its state variables based on the received input data; obtaining a combination of residuals from the estimator, each residual being associated with at least one observed NSS signal; and estimating an expected accuracy based on the combination of residuals and/or information derived therefrom. Systems and computer programs are also disclosed. Some embodiments may for example be used for safety-critical applications such as highly automated and autonomous driving.