## 8 Conclusions  
We have provided an overview of the capabilities and operation modes with our versatile photoelectron spectrometers sxPES and hxPES. Auger-Meitner lines have been used to demonstrate the resolving power of the instrument and for calibrations. Software devices have been developed and are continuously being improved with additional features for automation and to provide users and machine operators with online spectral distribution and polarimetry. The scientific impact is that pulse-resolved spectral information enables more detailed data analysis from user experiments. An additional important application that demands non-invasive photon diagnostics is that the online spectra provided by the PES can be used as a veto input for detectors to avoid recording data with undesirable spectral characteristics.  
Conceptualization, [PERSON] ([PERSON]) and [PERSON]; methodology and formal analysis, D.E.F.d.L.; software, D.E.F.d.L., I.K. and P.S.; investigation, [PERSON] ([PERSON]), N.K., [PERSON] ([PERSON]), N.G., S.K., S.S. and T.M.; resources, F.D.; data curation, P.S.; writing, [PERSON] ([PERSON]); visualization, [PERSON] ([PERSON]); supervision, [PERSON]; project administration, [PERSON]; funding acquisition, [PERSON] All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Data available in a publicly accessible repository: [[https://doi.org/10.5](https://doi.org/10.5)]([https://doi.org/10.5](https://doi.org/10.5)) 281/zenodo.13797536 accessed on 15 October 2024.  
Enabling operation of the photoelectron spectrometers was an effort by many individuals and groups. The design, construction, installation and commissioning was performed by XPD in close collaboration with the following scientific support groups from European XFEL and DESY: X-Ray Optics (XRO), Vacuum (VAC), Electronic and Electrical Engineering (EEE), Information Technology and Data Management (ITDM), Controls (CTRL), Data Analysis (DA), Survey and Alignment (MEA2) and Transport group (MEA5) have all provided valuable support. We acknowledge the operation of the European XFEL facility for providing beamtime. We have also benefited from feedback from the SQS, SCS, FXE and SPB/SFX instrument scientists for improving the online data analysis, and we acknowledge helpful discussions with our accelerator colleagues. Additionally, we greatly appreciate the discussions with [PERSON] and the contributions from PETRA III staff, in particular [PERSON] for supporting the initial tests at the P09 beamline.  
Author [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] were employed by the company European X-Ray Free-Electron Laser Facility GmbH which is a scientific institute and non-profit organization, and the institutional structure is a society of limited liability.  
Figure 7: DOOCS panel for online polarization monitoring. The target gas is krypton, and the selected photoemission line is Kr 3d. Pink bars indicate the integrated intensity over each of the 16 detectors. The green curve is the fitted Equation (8). Polarization is linear horizontal.