I don't know either, but a lot of geology is careful observation and you first record everything mentally and take notes about the important stuff and to create memory joggers. You might think tracking is a lost art, but when you are doing field geology far from help keeping track of what kind of poop is on the trail, disturbances in the natural environment, and tracks whether they be animal, human, or vehicle is important. A big pile of really fresh bear poop (generally filled with remnants of whatever berry it has been eating) means you are at the end of the traverse, at least for now, for example. Having worked in this highly observational field for forty plus years she rarely misses anything including eyelashes or lack there of. That stated I Imagine you are right that the Z-Stack eliminated some deficiency.