Discussion of the GEKS method is spreading in Europe and globally. Many NSO’s are already testing the GEKS and other multilateral methods or are aiming to test these newly proposed methods. But what about the documentation that clarifies how to implement new method to the calculation of the...

Differences between chain and base methods (or strategies) are analyzed. This is a preliminary paper that concentrates on numerical results and new ideas. Omitted proofs will appear in later papers. As in title, we use the term circular or chain error. We do not use milder terms as drift or...