  Central frequency is a key parameter of storage rings. This paper presents
the measurement of central frequency of the HLS-II storage ring using the
sextupole modulation method. Firstly, the basis of central frequency
measurement of the electron storage ring is briefly introduced. Then, the error
sources and the optimized measurement method for the HLS-II storage ring are
discussed. The workflow of the self-compiled Matlab script used in central
frequency measurement is also described. In the end, the results achieved by
using two methods to cross-check each other are shown. The measured value of
the central frequency demonstrates that the real circumference of the HLS-II
storage ring agrees well with the designed value.
