I want to print a paper copy of my book for editing. I like how it inserts the project title in the header, but is there a way to add the name of the chapter automatically to the header as well?
No, having section headers like that is a big layout job beyond Scrivener’s scope; you’d need to compile and then do that formatting in a word processor that could handle it. You can insert the titles at the start of each chapter, if you want, by checking the “title” box in the formatting section of compile for the appropriate file type (e.g. if each text document in your draft is a chapter, check the box in that row; if several documents together comprise a chapter and are contained in a folder with the title chapter, check the box to compile folder titles).
If you’re only compiling one chapter at a time, you could of course put the title of that into the header by just typing it into the box in the page settings pane of compile. The issue is just having the heading change based on where various documents begin and end, which is a complicated process. But if it’s all the same chapter, the title wouldn’t change. You’d need to type it in for each chapter when you compiled it, but if that’s not a big deal then it’s certainly doable. You could also use the tag <$compilegroup> in place of the actual title, if your chapter text is contained in subdocuments of a “Chapter” folder or document. That folder would then be the compile group that you would select in the contents pane of compile, and its title would get replaced dynamically for <$compilegroup> just like your project name is now substituted for the <$projectname> tag. In that case you wouldn’t have to change it every time you compiled a different chapter.
If I can format the header with the book title, why is it so hard to include the current chapter title?
To add the book title, launch the Compile editor, then double-click your custom format. In the format editor, click on Page Settings on the menu on the left, and activate the Header and Footer Text tab. There are text boxes for both header and footer. If you want to put the book title centered in the header, enter <$ProjectTitle> in the center box for the header. For the title of the enclosing folder, enter <$pageGroupTitle>.
Note that the original thread predates the current version of Scrivener, in which the Compile command has been significantly enhanced.