In the embodiment of FIG 6A, the heads 510 b, 510 r and 510 y of the laser sensors are positioned in an equilateral triangular placement which facilitates {HEAD ~ a three point plane distance determination} for measuring {TAIL ~ the height} of a surface such as a wafer surface 
In the embodiment of FIG 6A , the heads 510 b , 510 r and 510 y of the laser sensors are positioned in an equilateral triangular placement which facilitates { HEAD ~ a three point plane distance determination } for measuring { TAIL ~ the height } of a surface such as a wafer surface
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH