W-Speed--Finally Did It: Spreadsheet to easily calculate 0.3G speeds. BACKGROUND: Jones showed pictures to 200 people. They chose the best ones. The negatives from the best pictures were analyzed and all showed lowest useful density to be at the tangent of a line with slope zero point three times the gradient of the straight line portion. (0.3G). Current ISO standard is based on this work. For reasons not to go into here, the modern ISO test involves development to exactly a specific slope, then testing for 0.1 above film base. That is fine, but in HOME TESTING, you would need to zero in on that exact slope with repeated development tests before your 0.1 point matches the ISO standard. (not a big deal for personal film speed testing, but if I want to make a post about how fast a Chinese film is compared to Tri-x I should use an ISO method). Wouldn't it be great to have a way to test for relative film speed (for comparing emulsions) that you can get from a single curve of just about any gamma? There are TWO ways in the literature to do that. The DELTA-X way and the less-known "W speed." Steve has done a lot to explain the DELTA-X and indeed that is a fantastic way to do it. This method complements the work Steve has done promoting DELTA-X method and is presented as "another interesting way to do it." Why did I embrace the "W speed?" Because it is based on SLOPE and X-Intercept which are the two parameters I have been using all along for my relative film speed testing. (See link to extensive discussion of various computerized methods of film analysis http://www.apug.org/forums/forum37/78241-film-curve-plotting-fitting.html). Also, Steve has already posted extensively on Delta-X, so I wanted to do something a little different . BTW I want to thank Steve the literature he sent me so I could research 'inertia.'