[en] AWE (UK), IRSN (France), LLNL (USA) and ORNL (USA) began a long term collaboration effort in 2015 to update the nuclear criticality Slide Rule for the emergency response to a nuclear criticality accident. This document, published almost 20 years ago, gives order of magnitude estimates of key parameters, such as number of fissions and doses (neutron and gamma), useful for emergency response teams and public authorities. This paper will present, firstly the motivation and the long term objectives for this update, then the overview of the initial configurations for updated calculations and preliminary results obtained with modern 3D codes. Regarding the calculation of the prompt doses, the results from the modern tool used for this update are consistent. For the initial 2D configuration, the modern 3D tools results confirm the results obtained with the 2D tool used to create the 1997 Slide Rule. The impact of the use of new nuclear data is not visible on the update, with regard to the relative error (generally 5%). The interest of 3D capabilities will be developed for new configurations other than the initial five unreflected spherical uranium systems