that webbased calculation is a nice utility, but using those numbers is just one special case if you want to produce all circuits to get equal amounts of all the 7 kinds of science. In that case (and for 2k science), we need 3362 purple, 13672 red, and 18458 green which can be rounded to 3/13/18 or (like you did) 3/14/19.
producing the same amount of all science might be desirable for a megabase to achieve such a goal of xx kilo science per minute, but most techs require not all 7 science types, or different amounts of science per type. near the start of a map, the first three "traditional" sciences (red, green, blue) would only require 0 purple, 714 red and 2857 green for a ratio of 0/1/4 (or to have a bit larger numbers maybe 0/5/20).
and for another "mega achievement" (produce one of EACH item in the game, un-moduled, not including science types), the values would be 4206 green (including those for red and purple: 38554 k green), 2726 red (including those for purple: 5134 red), and 1204 purple, for a ratio of 1/2/4 or 5/11/17. the numbers get even more complicated when not one of each type shall be made, but one stack (of varying size) or even one chest full of those items.
to me it seems as if the numbers are quite subjective: all big bases have tons more green than red cicuits, but most of them are used for making red and purple circuits and thus are not included in the numbers of this special machine. when taking only the numbers for the circuits that are needed directly (instead of indirectly for green->red->purple), only a fraction of green is needed and "good ratios" seem to be in the range of 3/15/20 to 5/10/15 (2x or 3x as many red than purple, and only 50% more green than red).
of course, any fixed ratio for so many different items can never be exact and can only serve as a base production, having some additional assemblers to produce the exact needed numbers, similar to fixed ratio at oil refineries and then using heavy->light->petrol to adjust the amounts depending on current situation.
the other mod that produces all components for rocket parts has a much easier ratio since everything is directly used to make rockets and nothing else, thus having a fixed ratio only.
