This is wrong. SBR was defined correctly by Don and it is the inherent contrast range caused by the illuminance in the subject. When you plot identically exposed films to different times you obtain a range of what Davis calls average gamma, not a range of SBRs. If you wish, you can then plot SBRs against average gamma to obtain a correlation. SBR is not a value you can target, IOW you cannot say I am going to develop for an SBR of 6. AT least not in the way Davis has explained the BTZS.
Originally Posted by jdef