This query falls awkwardly between "Enlarging" and "General Exposure", but as the main aspect specifically concerns darkroom exposure, I've put it here. I use mostly roll film and while I hold the Zone System "in mind" when taking photographs (in the sense of being mindful of where I'm expecting my tones to "fall"), I'm not a "scientific" photographer, and any one roll is likely to have a wide variety of lighting and contrast scenes on it. But I'm trying to improve the consistency and printability of my negatives, and I've read Barry Thornton's "unZone" article a few times, and find it largely clear and potentially very helpful (http://www.awh-imaging.co.uk/barrythornton/unzone.htm). On p.4, he says the following: Now I think I understand why he might say this (is it to do with the way the paper will respond as if being "flashed"?) - but I am likely to be wrong in this, and if so would like to understand better what's going on here. So, in sum - why might a single 10-second exposure give greater exposure than 5 2-second exposures?