The light curve of the symbiotic nova HM Sge in 1960–1988 derived from 260 photographic and 243 photoelectric observations (Arkhipova et al. 1989) in presented in Fig. 1.
The rate of nova-like brightness increase in 1975 was about 0.04 mag/day. The maximum duration was about 4 years, with brightness oscillations of up to 1 mag. After 1981 the star brightness decreased slowly (at the rate of ~ 0.08 mag/yr) with small oscillations of 0.2 mag in the B band.
Fourteen years before the outburst of HM Sge a preoutburst phase with a light amplitude of 1 mag and a duration of about two years was observed, but its reality is rather doubtful. Similar features can also be seen in the light curves of the symbiotic novae V1016 Cyg and V1329 Cyg, 15 and 12 years before their outbursts, respectively.