As long as the GPS receiver outputting the RTK signal sends the NMEA data strings FW Mobile will pick up RTK quality automatically once the external GPS is connected. When going to the file menu and selecting GPS settings, Source Tab should be GPS receiver on comport. Then select the Com Tab. Here you need to select the correct comport the external receiver is plugged into, and enter the correct Baud Rate the receiver is outputting. This depends on the manufacture. Mobile will receive up to 10 pings in one second and use the highest quality signal of those 10 pings to use in logging. Mobile does not have a setting to pull on the most accruate, but there is a setting to state to only log when receiving RTK. However, when using automatic logging, you may want that correction set a little lower, Mobile will still log the best signal it receives, but if for a second we loose RTK, it would still keep logging with best signal without interruption. While still in GPS settings go to the Quality Tab to select your preference.