Defining Primary , Secondary , Additional Secondary Factors for RTCM Minimum Performance Specifications ( MPS )

HEA requires a high level of accuracy with 95% error levels of around 10 meters. To achieve such a performance, the eLoran user will require an additional secondary factor (ASF) grid and differential Loran. The grid corrections accounts for spatial variations in ASF. Differential Loran corrects for temporal variations in the nominal primary, secondary and additional secondary factors (PF, SF, ASF, respectively). As such, it is important to have consistent definitions of these factors. It allows for smoother transitions for different regimes of operations (such as from areas with and without differential Loran). It also gives receiver manufacturers and service providers a common standard so that ASF grids and differential corrections can be generated in a way that can be consistently applied throughout the world.