The original design was radical. However, as the typeface evolved, Renner and the foundry realized that strict geometry was not always conducive to comfortable reading. A perfect circle "O" can create awkward optical effects in blocks of text. This realization led to the development of the various weights, including the crucial "Book" weight.
Do not search for free downloads of "Futura ND Book." Because it is a premium restoration, it is frequently counterfeited. Free versions often lack the hinting, contain broken glyphs, or are actually old, buggy PostScript Type 1 files. futura nd book
Report compiled based on typographic reference data from Neufville Digital and comparative typeface analysis. The original design was radical