Oh!
This is a retroseries plotter.
Handy... juggling three resources on a basic calculator just isn't worth it, and I often just eyeball it instead.
From the title, I thought it was something to calculate when it would be worthwhile to upgrade your resource facilities or build a bonus multiplier facility, rather than to keep building more extractors.
What would you change the title of this topic to? the new calulator is not my favourite, but the old one works for me best, and I build most big ships in one turn!
I always use the build-in windows calcm usually my ships need two retrofits until they are ready though. Like the "hull" can be build in 2 turns, and two more are spent for retrofitting, so they will be ready after 4 turns, given enough repair capability.