I'm doing linear combination fits using 10 standards total, and choosing to use at most 3 or 4 standards in the fit. The problem is that depending on which I choose, 3 or 4, the results vary significantly. Often one standard will show up in one fit using at most 3 standards and not in a fit using at most 4 standards. For example: Unknown A: Fit using at most 3 standards Standard 1= 0.213 Standard 2= 0.374 Standard 3= 0.413 Fit using at most 4 standards Standard 1= 0.282 Standard 2= 0.269 Standard 4= 0.102 Standard 5= 0.346 Unknown B: Fit using at most 3 standards Standard 1= 0.278 Standard 2= 0.745 Fit using at most 4 standards Standard 2= 0.694 Standard 3= 0.117 Standard 4= 0.227 Note that the same 10 standards are run in each case, its only the number I choose to use in the best fit that is varying. As you can see, hopefully, the results vary significantly. Any ideas as to why this might happen? Any advice you can give on attaining more consistent results would be greatly appreciated. Thank you! Skya Fawcett PhD Candidate Department of Geological Sciences and Geological Engineering Queen's University, Kingston, Canada