What I did was use this website to pick 2 sensitivities. http://www.mindspring.com/~alanh/fracs.html So for example with my sensitivity: http://imgur.com/a/KeOU0 With an ADS sensitivity of 2 I would use an xfactor of 0.442062 for acog and 0.728940 for ADS. Plug these into wolfram to find the ratio: http://www.wolframalpha.com/input/?i=0.442062%2F0.728940 0.606444974895053090789365379866655691826487776771750761379 and put that into the site:   57/94 is the closest I can ge