I think the short answer is that most people don't control it to an exact number at all time. Probably more likely that they "float" around in an acceptable range of something like +- .5 Dkh, or maybe even +- 1 Dkh over a longer span.
I have a ton of stuff in the mix when it comes to supplementation/dossing. I have a Carx that is rock solid constant (Apex control, high end Co2 regulator, and Masterflex pump). I also have a 2 part dosser set up that is controlled by apex to dose during the highest consumption part of the day.
I also have an Alkatronic testing Alk 6 times a day, so I am way past daily testing, I know the value almost continuously, and have had it testing as much as every 2 hours. My max swing is .2 over the course of a day, and .4 over the span of months.
I also have 100+ acros in my 400g system, so high consumption is pretty much a given, and the reason I monitor so closely.
Even with all this in place, I still float around a little.