You're right, the dots are the exact values, and I have the "original" ones for both data sets.

Since the two sets are very different in the scale of the values, I needed two Y axes to be able to visualize them on one chart. So I did input the exact values I had, although Google Sheets calculated the values to actually be displayed on the second Y axis for it to match the first Y axis better.

However, I'm still needing the actual values Google Sheets plotted for the second Y axis, since I need to redo the chart on another program that doesn't have the automatic two-axes function. So I need to figure out what function Google Sheets used to calculate them so I could calculate them myself.

The cubic spline looks very confusing at first glance, but I'll look more into it, thank you!