In the embodiment of FIG 6A, the heads 510 b, {TAIL ~ 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 {HEAD ~ a surface} such as a wafer surface 
In the embodiment of FIG 6A , the heads 510 b , { TAIL ~ 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 { HEAD ~ a surface } such as a wafer surface
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL 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 OTH OTH OTH OTH OTH