Effect of noise at various phases on the C iiλ6580 absorption notch. The top row depicts the neighborhood of the feature as observed by SNIFS. Each successive row simulates progressively noisier observations, with the S/N per Å labeled at right. The red vertical line depicts the center of the C ii notch to guide the eye. Early observations are no guarantee of a C ii detection even if it is there at lower S/N but generally the feature becomes harder to discern with time as the notch amplitude decreases. Wavelength and flux scales depicted are the same in each panel.