[Bill Burk]

Now I'm trying to understand the previous discussions. What exactly does it mean 'shaded palm in Zone IV'?

Correction - it's not a typo...

With a reflective meter, you can meter the light falling on a scene by holding your hand up to the light and meter your palm and "place the palm of your hand" on Zone VI, because this is correct exposure for the most pleasing pictures of people.

(Placing a meter reading on Zone VI means to open up one stop from meter reading).

Minor White described a shortcut metering technique similar to the BTZS techniques, and the shade reading is what was meant by that quote.

But contrary to normal "palm" placement, instead of opening up one stop from the shadow-based reading of your palm, you close down one stop. Believe that is because the shadow area of a photograph does not require the full exposure to be realistic.