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In this study, we present an analysis of over 34 years of observational datafrom CAL 87, an eclipsing supersoft X-ray source. The primary aim of our study,which combines previously analysed measurements as well as unexplored publiclyavailable datasets, is to examine the orbital period evolution of CAL 87. Aftermeticulously and consistently determining the eclipse timings, we constructedan O$-$C (observed minus calculated) diagram using a total of 38 data points.Our results provide confirmation of a positive derivative in the system'sorbital period, with a determined value of $\dot{P}=+8.18\pm1.46\times10^{-11}$ s/s. We observe a noticeable jitter in the eclipsetimings and additionally identify a systematic delay in the X-ray eclipsescompared to those observed in longer wavelengths. We discuss the interplay ofthe pertinent factors that could contribute to a positive period derivative andthe inherent variability in the eclipses.

Revised ephemeris and orbital period derivative of the supersoft X-ray source CAL 87 based on 34 years of observations