Not quite sure I understand the levels adjustment panel in Photos.  I understand the typical curves dialog, because I understand which axis is input and which one is output and how any given curve impacts the image.  Thus I understand how the common S-curve works.  But the levels dialog, is the top line “input” and the bottom line “output”?  How would I move the first-quarter and third-quarter anchor points to mimmick the standard S-curve”  I’m assuming pull the bottom anchor points both closer to the middle?  Or is it closer to the ends?

I’m trying to mimmick my default Aperture import preset, which includes a mild S-curve which I want to get reasonably close to replicating with Photos.

And yes, still pissed Apple doesn’t allow me to define a custom adjustment preset!  How could they have not thought to do that?