In the marked metric graph model of Outer space translation length functions can be interpreted as follows. Let "T" in "X""n" be represented by a marking "f" : "R""n" → Γ with a volume-one metric graph structure "L" on Γ. Let "g" ∈ "F""n" = 1("R""n"). First push "g" forward via "f"# to get a closed loop in Γ and then tighten this loop to an immersed circuit in Γ. The "L"-length of this circuit is the translation length formula_23 of "g".