I believe the three sections are dependent on the type of air bleeds and where they are located.
Some carbs have IDLE AIR BLEEDS in the top casting (air-horn) and some have 2 idle airbleeds in the main casting. So this means you need to choose which one pertains to the carb that you have.
Then to make things more complicated there are 2 different types of MAIN air bleed setups, one has 2 main airbleeds (1 in the main casting and 1 in the airhorn). Then thre is the other type that has a SINGLE main airbleed in the airhorn. So it seems like there is 3 sections but really there is only 3 variations and you need to choose which one is applicable to the carb you are working on.
Just use the information in a recipe (from recipe 1,2 or 3) that pertains to your carb.
The first thing you have to do is determine what you have. Read the section on idle circuits and main circuits very carefully. The pictures show exactly where everything is, (Cliff did a great job on this feature of the book), then you can proceed with the modifications to set your carb up so that it will match your engine. ANyway, goodluck and enjoy!!