| http://www.w3.org/ns/prov#value | - FIG. 2b shows the especially preferred embodiment described above with respect to FIG. 1, wherein two light sources 5 and 6 illuminate a common defined area of measuring plane 2 and have associated therewith single detector 7 disposed on the opposite side of plane 2 which detects both radiation from red-light source 5 transmitted in the bright field and IR radiation from source 6 transmitted in th
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