Since 2001, Global Systems Science (GSS) books have been designed for easy reading both on paper and on computer display.
If you use text-block/graphic arrangements shown here as "Desirable Layouts", the reader will never have to scroll up to read from the bottom of the first column to the top of the second column. They can keep scrolling down continually.
On the contrary, "Undesirable Layouts" are "forbidden" since they force the reader into the undesirable up/down scrolling when reading from column to column.
It's fine to have parts of a page that have 1-column text blocks, but it's best to still keep the column width significantly less than the full page width, since it's much harder to read very long lines of text.
Other arrangements are possible: you can have 3 columns (appropriate for even smaller font sizes in hard copy). Just apply similar principle (imagine reader viewing only 1/2 page at a time—top/bottom) and it will be just fine. Each half page can be a readable "page unit" unto itself.
Starting in 2010, all the GSS books were converted, chapter by chapter, to web pages. To facilitate printing books on paper, there are "print-friendly" versions, one chapter per web page.
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