1 INTRODUCTION  
2 MASS FUNCTION AND BIAS OF DARK-MATTER HALOES  
3 FIDUCIAL MODEL  
4 FROM HALO MASS TO X-RAY PHOTON COUNTS  
5 THE eROSITA EXPERIMENT  
6 OBSERVABLES  
7 FISHER-INFORMATION FORMALISM  
8 RESULTS  
9 DISCUSSION  
12 CONCLUSIONS AND SUMMARY