If you have a dt line it will have 3 distinct diameters ( as well as transition diameters between them) If the tips both have a diameter that corresponds to say "H" and the belly has a diameter that is equal to say "C" you then have an HCH line. WF lines are designated the same but naturally the tapers would be different -- such as HCF.
One thing to keep in mind is that this system only establishes the diameters of the line at it these points. It does nothing to define how long these sections are. Post war (WWII) there was a lot of experimentation by line manufacturers. It was not uncommon for two lines with the same designation to be quite different because one manufacturer chose to make a long tip and a short transition to belly and the other made a different length tip with a longer transition.
If this is something that interests you, I would recommend McClaine's "The Practical Fly Fisherman". There is a whole chapter devoted to lines and pages of taper comparisons between manufacturers. And a darn good book too.
AgMD