Can anyone please explain me the value of Log H Ref given in most of Kodak Tech. Pub. Characteritic Curves? E.g. Ektar 100 E-4046 curve gives a Log H Ref of -0.84. Is it middle gray when shooting at box speed? Isn't middle gray normally placed at log 0? Compared to E-4040 Log H Ref -1.14 the Portra 160 VC seems to handle an enormous overexposure of nearly 7 stops.