Recently acquired a Sinar F+ (a shiny metal F1), and although the basic operation is more than intuitive, I have a few questions about some details.

1.) I understand the depth of field calculator. (Which is a moveable wheel around the geared focus adjustment on the right side of the rear standard. Stated here because there seems to be more than one version of this analog calculator.) But what are the degree marks for on that same fine focus adjustment? I mean the degree marks from -20 to +10.

2.) On the lower left of the front standard there is a small octagonal hole tapped by a threaded set screw. The screw has a thumb wheel for easy access. What's this for?

3.) Which of the controls on the Sinar F series is the plastic piece that many complain is too easily broken?

I've written Sinar for user manual, but I want to use the camera asap, hence the questions.

Thanks in advance, BAB