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 a three point plane distance determination for measuring the height of {HEAD ~ a surface} such as {TAIL ~ a wafer surface} 
such as
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 a three point plane distance determination for measuring the height of { HEAD ~ a surface } such as { TAIL ~ 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL