Oh me oh my. I don't know.
OK, seeing the picture makes me inclined to think that planities is intuitive enough.In this context we are describing the relatively flat part of a respiratory pressure curve.
I don't really know. I'm a little out of my depth with mathematical things.What do you think about algorismus?
Not sure if you want to stick with extant Latin terminology, which might make this process difficult. Perhaps, if you want to be creative, you could use perdatum, a possible substantivization from a hypothetical perdatus "given through"?The first is "Route", as in, "By what route was the drug given". Would via work do you think? The suggested Spanish translation was ruta.