Here's another good paper that covers pretty much all of what your asking also. http://www.soil.ncsu.edu/programs/nmp/Nutrient Management for CCA.pdf
You'd asked about how nutes are calculated and what they are measured in. For the most part, the measure depends on the area of industry we are talking. In agriculture they go more by Lb/acre (or hectare), however in this specific field they "typically" refer to either % or ppms. If looking from a tissue point of view Nitrogen is often expressed in percent or brands of nutrients are also in percent. When considering nutrient profiles or formulas, all of the elements are "typcially" expressed in ppms. The local "Chem dude" @squiggly, prefers expressions in moles (for solutions), I believe.
When I first provided fatmans' thread above; I was not intending to be sarcastic, but that he does show a chart with "common forms available" for each element (N,P,K,Ca). The paper I just linked in this response also covers common available forms as well. Fatman did not include Urea in his list as that's not typically practicable for much of this industry, however between his chart and other linked papers so far; you should have all common forms. Many times these elements can be found in additional compounds, but are not useable for plants; so in general, there's a small group of things that are used.
I'm not sure if you can make a nutrient building guide for dummies, per se; as building profiles from scratch is more complicated than buying pre-made brands (as it were). On top of just building aspects alone, there are so many variables that change what a plant needs in situation A vs situation B. If a person was to purchase "pre-made" brands, then the mfg. has already done the "building" work and adjusted things for whatever that product is sold for (e.g. coir vs soil vs hydro). If a plant does not grow well with a particular company, then many will try another brand or combo of brands. This kind of switching is much easier to do (and have success with) versus trying to build from scratch or even adjust something off with brand X. To really be able to build things from scratch or even adjust pre-made formulas; a person should have a more complex understanding of nutrient requirements, mediums, environments, diagnosis etc. So, I'm not sure all this could be wrapped up in a "for dummies" guide without the possibility of creating more problems for a grower. As, @Seamaiden says: "don't go chasing numbers" and it is a wise statement.
Now that I've given the proper, "do not try this at home" talk.... If a person still wants to delve into building "profiles" and adjusting things themselves; there are "calculators" available for this to be done. All elements would be measured in Grams or Ml for ingredients and have ppms for all elements on the output. If a person gets into building profiles, then they also need to have target points to reach. Again these target points are going to vary with each situation but there are literally hundreds (if not thousands) of forum pages; regarding this specific topic. Many times profiles are started with, or adjusted by tissue sample testing and many profiles are based off these. Here again though, it would be impossible to condense all of these down to a simple 1+1=2 scenario. Because of this, not many people provide their profiles nor do they tend to suggest such; beyond certain "basic" ratios that is. Often the best advice you'll here, is that the ratio of elements is the most important and in the end; that is the larger truth.
