The astrometric global solution is a principal component of the final star catalogue. Itis the solution of a relatively complex least-squares problem related to Gaia’s designthat can only be solved using an iterative process. Hopefully we found an efficientconverging algorithm with a robust stopping criterion. Nonetheless the usage of aniterative algorithm imposes some limitations on our knowledge of the statisticalproperties of the solution such as the variance which need to be investigated furtherthrough simulation techniques.