There is a massive gap between Immortal-grade cultivation techniques and Divine-grade cultivation techniques.
According to Lu Feng's deduction, if he wanted to upgrade the Chaos Divine Formula he practiced from the lower Divine-grade to the middle Divine-grade, it would take at least ten Immortal-grade techniques to fuse together.
However, if he used Divine-grade techniques for the fusion, just a single one would be enough to elevate it by a small tier.
Chapter 288