Sacarino111's post in Waypoint programming in Nevada NTTR map was marked as the answer
Hi. Yes, in Nevada you have to enterWest for Longitud. The thing is as follows: once entered the North coordinate, dubber down for Longitud and press the "4" button in the ICP for "W" and then the normal XXX.XX.XXX numbers. Then ENTR, as normal and the the altitud. Tis should do the trick.