I read many previous posts and could not find a clear answer to my question, although I'm sure someone will find it somewhere, so please excuse. For clarity, I understand logs, fstops, etc. A film like Fuji Velvia gives the x-axis for its characteristic curve in ABSOLUTE terms. Velvia 100 https://asset.fujifilm.com/master/e...f98b7d489c2/films_velvia-100_datasheet_01.pdf Velvia 50 https://www.ishootfujifilm.com/uploads/VELVIA 50 Data Guide.pdf For velvia 100, an absolute exposure of log(lux*sec)= -1 results in a density of 1. For velvia 50, the exposure resulting in the same density is approximately -0.7, which is approximately 1 stop more of exposure. Which makes perfect sense. Some films, such as ilford HP5 400, give the x axis as relative log. In either case, I can figure out the approximate exposure latitude of the film in stops, but what about latitude to over vs under exposure? Where is the anchor point for exposure or density, relative to "correct" exposure? Based on the table provided in this website, if (log) exposure is given in absolute terms, -1 yields the correct density for middle gray for iso 100 film. -1.3 for 200, etc. Thus, one can figure out how much under or over exposure can occur before the density stops changing linearly. It may be asymmetric, which is why knowing the "anchor point" is useful. https://www.filmshooterscollective....ide-to-using-film-characteristic-curves-12-25 What about "relative" log exposure? I've seen some kodak reference sheets refer to "log H ref." Thanks all.