1.1 New for Cycle 34

We have made the following updates to the WFC3 Instrument Handbook for this cycle:

• We updated information, plots, and references throughout the handbook based on the Instrument Science Reports (ISRs) released in 2025.
• We added Section 3.3.6, including Figure 3.8 and Figure 3.9, to compare select WFC3 bandpasses with Roman/WFI filters. 
• We discussed recent WFC3/UVIS saturation analysis in Section 5.4.5, and replaced Figure 5.6 with the updated saturation map currently used in the calibration pipeline.
• We used new WFC3/UVIS gain data to update Section 5.4.6, including Table 5.3 and Figure 5.7.
• We improved scaling on the WFC3/IR pixel-to-pixel flats shown in Figure 5.28. 
• We replaced Section 5.7.5 and Figure 5.29 to reflect updated WFC3/IR linearity correction calibration.
• We added a column for the cumulative throughput width for WFC3/UVIS filters and grism to Table 6.2.
• We reorganized Table 6.4 to show how WFC3/UVIS quad filters are grouped together in the filter wheel.
• We discussed issues with extrapolating WFC3/UVIS encircled energy curves for small apertures in Section 6.6.2. 
• We added to Section 6.6.3 a brief discussion of fine-guidance jitter and its impact on the PSF. 
• We clarified the significance of WFC3/UVIS extended pixel edge response (EPER) imaging in Section 6.7.2. 
• We added references to new PSF extraction and modeling tutorials to Section 6.11.4. 
• We added a column for the cumulative throughput width for WFC3/IR filters and grisms to Table 7.2.
• We calculated JWST/NIRCam limiting magnitudes and added them to Table 7.10.
• We updated Section 7.9.6 and Figure 7.15 to encompass the latest WFC3/IR blob analysis. 
• We added new Cycle 34 guidance regarding grism direct images to Section 8.3.
• We discussed in Section 8.5 previous, current, and upcoming software tools for grism spectral extraction and calibration, and also added details about spectral dispersion from off-frame sources. 
• We updated Section 10.2, Section 10.3, and Section 10.4 to reflect changes in guidestar acquisition, overheads, and orbit times under reduced gyro mode (RGM). 
• We reviewed new analyses of the temporal evolution of WFC3/UVIS and WFC3/IR geometric distortion in Appendix B.1. 
• The following changes have been made to Appendix E:
  • We added the Cycle 33 calibration plan and time span to Table E.1 (Section E.1).
    
  • We added a summary of the WFC3 calibration plan for the current Cycle in Section E.20.