This concerned the determination of mean and extreme proportion expressed in perspectival constructions - the perspectival ladder of Brunelleschi, Alberti and Piero della Francesca, an alternate adaptation of the machine of Eratosthenes for finding two mean proportionals, also described as the mesolabium in Vitruvius, Book IX.
Ang pag-aalala sa pagpapasiya ng ibig sabihin at matinding katapat nakasaad sa perspectival constructions - perspectival ang-ledder ng Brunelleschi, Alberti at Piero della Francesca, isang kahaliling adaptation ng makina ng Eratosthenes para sa paghahanap ng dalawang ibig sabihin ng proportionals, inilarawan din bilang ang mesolabium sa Vitruvius, Book IX .