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