  We report on the preparation of and calibration measurements with a
$^{83\mathrm{m}}$Kr source for the CENNS-10 liquid argon detector.
$^{83\mathrm{m}}$Kr atoms generated in the decay of a $^{83}$Rb source were
introduced into the detector via injection into the Ar circulation loop.
Scintillation light arising from the 9.4 keV and 32.1 keV conversion electrons
in the decay of $^{83\mathrm{m}}$Kr in the detector volume were then observed.
This calibration source allows the characterization of the low-energy response
of the CENNS-10 detector and is applicable to other low-energy-threshold
detectors. The energy resolution of the detector was measured to be 9$\%$ at
the total $^{83\mathrm{m}}$Kr decay energy of 41.5 keV. We performed an
analysis to separately calibrate the detector using the two conversion
electrons at 9.4 keV and 32.1 keV
