HT/HS Methodology

LA (Lower Alabama)
After reading the excellent HT/HS threads (TS's current one and MolaKule's HT/HS Study thread) and looking at some oil spec sheets, I've become curious about HT/HS test methodologies. (A search didn't lead me to an answer ... if it's out there will someone please point me to it.) Pennzoil uses ATSM D-4683 to arrive at HT/HS numbers; Castrol uses CEC L-36-A-87 to arrive at theirs. Anybody care to share the relative advantages/disadvantages of the various methods and how they compare?