Illustration of telluric line corrections using an automated fitting method that takes stellar continuum, telluric lines, and also DIB into account. The black line is the original spectrum of HD 176853, the green line is the synthetic telluric transmission, the blue line is the fitting result, and the red line is the residual. The very strong telluric lines are not entirely removed, but the residuals do not significantly affect on the DIB equivalent width.