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