With the pwelch plotting estimate, what mathematically is being performed?

I've attached a screenshot of my window to demonstrate the script I'm using to plot the pwelch as well as the two options for plotting which are shown at the top of the window in the plotting tab.

I have data files (in Volts) which require the calculation 20*log10(data). Prior to implementing this script, I've averaged out noise and removed DC bias.

I cannot find in the Documentation what mathematically is going on here regarding fft implementation and if 10*log10 is being used instead of 20*log10.