I have a question regarding an article/paper I have read (https://www.electronicdesign.com/power/analyze-mosfet-parameter-shifts-near-maximum-operating-temperature) and hope someone can help me here. In this article the author describes an equation for the drain-source on-state resistance of a MOSFET as a function of temperature and drain current. Unfortunately, I am too stupid to understand a small but important step of the author. It is about the resistance coefficient a of equation 6. The author says "a is a resistance coefficient derived from the Point 1 voltage and current (Figure 2, at 25°C)", but I don't understand how exactly, he determines this coefficient. I tried some calculation, but I don't get the same results for a like the author (listed in table "SIMULATION RESULTS FOR FIVE MOSFETs" in the article/paper).
Has anyone read this article or understands the author at once? Many thanks in advance!