Developing more thoughts on PES

When composing this post about the College Board Webinar relating to PES in February of this year, I wrote; The things to take away from these much more complicated spectra for me, are two-fold; (i) Unlike in the simulated spectra, where the intensity (height) of the...
17 TOPICS, OR 6 OR 9 UNITS?

17 TOPICS, OR 6 OR 9 UNITS?

That sounds like a Chicago song, but … … in various places on this site, you will see references in the AP sections to “17 TOPICS”, “6 UNITS” and “9 UNITS”. This can be confusing, so here’s the background to those...