Telluric correction by two different methods for the cool bulge LPV star OGLEII DIA BUL-SC1 235. The black line is the original 1D spectrum extracted, and the blue and red lines are the spectrum after correction by the PCA reconstruction and the temporally-closest telluric absorption spectrum, respectively. The green spectrum is an M5III star with a similar temperature, HD175865, taken from NGSL as a comparison.