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