Immortal Alchemists had nine complete stages. The first three realms were collectively known as the Alchemy Venerables. The next three were known as the Alchemy Empyreans. And finally, the loftiest goal of many who followed this path, there were the Alchemy Gods.
Refinement techniques, known for their complexity, actually shared a level of difficulty with combat techniques an entire grade above them. This meant that Divine Grade Refinement Techniques were just as difficult to learn as Mystic Grade Refinement Techniques!
Of course, this was just an average and not an irrefutable rule, but it was widely accepted nonetheless.
[Heaven Soaring Nine Seals] was considered to be on the complete opposite side of the spectrum. It was the most difficult of the Lower Divine Grade Pill Refinement Techniques, dwarfing even many Mystic Grade Techniques!