1 INTRODUCTION  
2 THE CR-HR METHOD  
3 INGREDIENTS ENTERING THE CR-HR METHOD  
3.1 Modeling the CR-HR distribution of clusters  
3.2 Illustrative examples  
3.3 Generalizing: adding redshift information  
4 ACCOUNTING FOR MEASUREMENT ERRORS  
4.1 Including measurement errors in the CR-HR and $z$-CR-HR diagrams  
4.2 Comparison exercise: errors on the estimated cluster masses  
5 THE FISHER ANALYSIS  
5.1 Fisher formalism  
5.2 Results  
6 SUMMARY AND CONCLUSIONS  
6.1 Main results  
6.2 Future work