  Recently, Halpern et al. discovered an oscillation with a period of 464 s in
the cataclysmic variable 1RXS J230645.0+550816. I conducted extensive
photometric observations of this object to clarify the coherence of this
oscillation and to measure the oscillation period with high precision.
Observations were obtained over 22 nights in 2018 and 2019. The total duration
of observations was 110 hr. The oscillation was revealed in each long night of
observations and was coherent throughout all my observations covering 15
months. Due to the large coverage of observations, I determined the oscillation
period with high precision, which was 464.45600+\-0.00010 s. The oscillation
semi-amplitude was large and showed changes from 41.8+\-1.5 mmag in 2018 to
48.6+\-1.8 mmag in 2019. The oscillation pulse profile was symmetrical with a
noticeably wider minimum compared to the maximum and showed no noticeable
changes during 2018 and 2019. The high precision of the oscillation period
allowed me to derive an oscillation ephemeris with a long validity of 70 years.
This ephemeris can be used for future studies of oscillation period changes.
Although short-period X-ray oscillations have not yet been detected in 1RXS
J230645.0+550816, the intermediate polar nature of this object is very probable
due to the high degree of coherence of the 464-s oscillation.
