2 metres.
Edit: sorry, 2 metres is for RM2, and is fixed for grid generation.Contouring grid resolution is variable, depending on map size, and cannot be altered by the user.
In RM1, initial grid resolution is 1 metre and the grid resolution for contouring (using a downsampled initial grid) can be automatic or set by the user. In this case, the grid resolution is the selected number in metres.