HI all. Just wandering what coordinate system Emlid reach rs/ rs+ use? Is it possible to switch to say OSGB1936 and still be able to use RTKLib for PPK?

The reach receivers collect in WGS84 guys will always be the case with all current GNSS equipment. There is currently no way to report in another CRS. I can’t imagine it will be too long before this is possible, but we will see what all systems or integrated.