Ok, I have never been able to do this.
I have seen it done on tutorials but can never get the same result, and yet it seems so simple to do. As you can see from the image I want to align my verts to the grid.
I select them first, select the move tool, hold down x and move them. but the result is what you see here.
It seem that the average of the 3 verts is snapped to the grid only and not the verts themselves.
What am I doing wrong?