Yes you zero out the container you are using. Many buy deli food type containers for pints and quarts or real buckets for gallons (though you will almost always want a container at least half again as larger to make stirring easier)
Then, the Union software gives you volume options, with all components given in their corresponding weights. Zero between components.
The Union system you posted requires their inks. I believe that they have two or three different systems, all complete inks rather than the base and pigment systems like the Wilflex PC.
Complete ink systems are easier to use on really small amounts.
btw, I still use the Mixo system mostly because it includes formulas to match stock Union colors. I also often mix tiny amounts.