Using Reach for landsurvey and more

Addit: I after playing with this - it is quite easy, under RTKNAVI>Options>Positions - Base Station, Set the base station coordinates as your datum or the origin in archicad, Now the the crux --> Tick the antenna type (leave blank unless you have antenna calibration file) then adjust the (E)astings (N)orthing ie X,Y difference from your datum/archicad origin.This differences have to be in the North and East grid directions.