A method of reference position determination for a DGNSS base station. The adhesive sheet S is cut along the outer periphery of the wafers by a cutter blade 63 mounted at the free-end side of a robot 15. The insert assembly staggers the relative positions of adjacent spring contacts in the y-direction, and staggers the spring contact pivot points in the x-direction, yet maintains a common contact region for all the spring contacts for contacting the contacts of the plug.