The way it is described to be as precise as possible in the end result with making 5 litres 4 Dkh fluid from demineralized water and baking soda. Might be a tad not worth the hassle. What the heck are we going to do with 5 litres of that stuff? Providing 6 family generations over sufficiently stocked for multiple tank syndrome?
But if you happen to have a weight scale down to 0.01 gram (1 Cg) you can come pretty close to making smaller volumes.
Of course the smaller the volume to mix the more likely to make an error and end up with 4,3 Dkh. But then again how important is accuracy to the decimal for hobby use. the only way we have to check for Dkh is a drop tester 1° per 1 drop.
I didn't worry much about it and made 500ml 4Dkh fluid with the use of a Cg weight scale. And imho it worked like a charm. A 0.01 weight scale is € 11 maybe from Ebay and also something worth having in the toolbox. Fun to have fun to play fun to do, thus well worth it. Also use this weight scale to dry fert my tanks.