Quote Originally Posted by jdef

Are you familiar with BTZS? There is a procedure by which the SBR can be extracted from a curve produced by printing a stepwedge onto the film in question, and reading the resulting densities with a densitometer, and plotting them against the densities of the stepwedge itself, which represents the luminance range of a theoretical scene. The resulting SBR value is often not an even number. By processing identically exposed films to varying extents, a range of SBR values results. SBR is just one value of many that can be targeted.

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.