2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/115440We define the notions of unilateral metric derivatives and ``metric derived numbers'' in analogy with Dini derivatives (also referred to as ``derived numbers'') and establish their basic properties. We also prove that the set of points where a path with values in a metric space with continuous metric derivative is not ``metrically differentiable'' (in a certain strong sense) is $σ$-symmetrically porous and provide an example of a path for which this set is uncountable. In the second part of this paper, we study the continuous metric differentiability via a homeomorphic change of variable.21 pages, 1 figureClassical Analysis and ODEsMetric Geometry26A24; 14H50text