Line-Segments in Proportion: c Drawn Twice
'the two represent a single line'
Two sets of bracketed line-segments carry the paired values d 12, e 12; a 6, b 6; c 3, c 3; and f 6, f 6. A note explains that c, which appears twice, is not two lines but one: 'the two represent a single line.' The halving run 12–6–3 lays out a sequence of proportional parts. The figures are in pencil gone over with pen, within the notebook's Euclid-based proportion studies.
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c appears twice but is one line
The closing note states that the letter c occurs twice and that 'the two represent a single line.' The two c-marks therefore label the same segment rather than distinct magnitudes. The attached values fall in a halving sequence, 12, 6, 3.
Paired segments and their lengths
The segments are lettered d and e at 12, a and b at 6, c at 3, and f at 6, drawn in matching pairs. Grouping equal or halved lengths side by side is Leonardo's way of comparing the parts of a divided line.