The ORNL ion-atom merged-beams apparatus has measured benchmark electron capture cross sections for the multicharged ion C³⁺ on H(and D) from .30 eV/u to 3000 eV/u (C. C. Havener, A. Muller, P. A. Zeijlmans van Emmichoven, and R. A. Phaneuf, Physical Review A, 51, 2982 (1995)). Because of its importance, this system has been studied experimentally and theoretically in detail for several years. Carbon ions are one of the major impurity ions in magnetic fusion plasma devices. Energy loss from high temperature plasmas is enchanced by the radiations from impurity ions that have undergone capture to excited states. Low energy measurements of charge transfer for C³⁺ are also important for astrophysics, since the cross section is predicted to sharply increase at low (near-thermal) energies. The merged-beams measurements above 50 eV/amu show excellent agreement with the more recent 22-state coupled- channel molecular-orbital calculation by Errea et al. (J. Phys. B:, 1991) and below 50 eV/amu with the calculations by Herrero et al. (J. Phys. B, 1995). The results differ significantly from previous predictions and have consequence on the normalization of state-selective measurements (Wilke et al. J. Phys. B, 1986).