If you like to add a tablespoon per gallon and dilute from there, fine. I'm all for everyone doing things their own way. But that number they recommend (1 tablespoon) does not have anything to do with the N-P-K content in a quantitative way. Art made that point very specifically in the article. It is a number pulled out of the air to sell product. It does not help you standardize or calibrate anything. 1 tablespoon of product in a gallon gives a different nitrogen concentration for each of the three MG products (an almost 2 fold difference).
One manufacturer will disagree wildly with another if you calculate the ppm N of their recommended dilutions. There is no industry standard for this. Even within one brand you may have big differences, like Art pointed out. For what it's worth, as I have mentioned, those dosage recommendations are close to useless in the real world, if you're interested in using the minimum amount of fertilizer to achieve the desired results. Which I am, and I think most people should be. To put it another way, all the MG recommendations tell you is how much is more than you will ever actually need for any given application. The only numbers that are standardized are in the N-P-K rating.
The easiest way to arrive at a consistent dose is to actually calculate the amount you need for a certain ppm N (no math required, you just plug two numbers into the form on the page in the link, and it spits out how many tablespoons). Start low and go up from there until you get what you want. Or you can take what works with brand A and figure out what works with brand B by the relative amount of nitrogen in the formula. If you are not doing these calculations then you are basically guessing at the final absolute strength of your fertilizer. Which, again, is totally fine. But it is not quantitative.
Spreadsheets strike me as a way overcomplicated substitute for common sense and fuzzy logic (ie. add more when more is needed, add less when less is needed). Rather than following complicated instructions or rigid formulas I prefer to observe and adjust. But again, to each her own.
