The present invention relates to the identification and use of bone morphogenetic protein -binding domains of members of the repulsive guidance molecule protein family, and polypeptide fragments and fusion proteins derived therefrom. A functional module is capable of being inserted into the server chassis from the opening. Formed on the bottom surface of the substrate is a first encapsulation part. The spring, latch and housing are coupled such that the vertical channels capture and guide the interference fit tabs down the side of the housing as the foot members of the latch are inserted into the pockets of the housing. The pseudorange measurements provide a set of possible positions and the terrain model is used to identify the correct position amongst the possible positions.