Chapter 4: STIS Error Sources 4.1 Error Sources Associated with Pipeline Calibration Steps 4.1.1 Readout Noise and A-to-D Conversion 4.1.2 Bias Subtraction (only relevant for CCD observations) 4.1.3 Dark Current and Hot Pixels 4.1.4 Flat Fields 4.2 Summary of Accuracies 4.3 Factors Limiting Flux and Wavelength Accuracy 4.3.1 Flux Accuracy 4.3.2 Wavelength and Spatial Accuracies