Note 1 to entry: For a curve defined by the position vector $r=f(u)$ as a function of the parameter u, with an origin O corresponding to $u=0$, the abscissa of the point M corresponding to u = u_M is the line integral ${\displaystyle \underset{\text{O}}{\overset{\text{M}}{\int }}\left|\mathrm{d}r\right|}={\displaystyle \underset{\text{0}}{\overset{u_{\text{M}}}{\int }}\left|\frac{\mathrm{d}f}{\mathrm{d}u}\right|\mathrm{d}u}$.

Note 2 to entry: In the usual geometrical space, the abscissa along a curve is a quantity of the dimension length.