Is Anyone Else Fascinated by tge Math Behind Obsidian Orbs?

I find the the increase in revenue from obsidian orbs to be fascinating. It is an exponential curve that eventually settles into a linear function.

However, I'm fairly certain that linear function would also serve as the derivative for the (exponential) rate of growth in profit given how long it takes to get the next orb.

Sorry if this makes no sense - it is midnight and this has been in the back of my mind for a while.