Figure 10, p. 127, from (Wittkower, 1962/71).
Serlio's system of proportion, 1537 AD.
Here we recognise the symbol "O"
of Brunés.
However, in Wittkower's comment
on this figure on pp. 126-127,
he explains that the construction is only
used as a convenience to obtain
the rational ratios, 1:2 and 1:3.