Chapter 2: Special Considerations for Cycle 21 2.1 New FUV Detector Lifetime Position 2.2 Resolution of COS Observations below 1150 Å 2.3 Time-Dependent Sensitivity Changes 2.4 Non-Optimal Observing Scenarios 2.5 SNAP and TOO Programs with COS 2.6 Should I Use COS or STIS?