Joan, You must compensate FL1 (FITC) signals out of FL3 (7-AAD) on most cytometers indirectly. For example: On BDIS instruments compensation is via dual differential amplifiers where you sample FL1 and remove a percentage from FL2, sample FL2 and remove a percentage from FL1, and so on among adjacent channels. If you first balance FL1, FL2, and FL3 in terms of setting a similar sensitivity, then run compensation controls for FITC, PE and 7-AAD, the FITC that gets into FL3 will be essentailly removed when you sample Fl2 (PE only) and remove it from FL3 (7-AAD). If you are using *only* FITC and 7-AAD you still need to setup FL2 in order to remove the FITC from FL3. In this case you run FITC but use FL3 - FL2 to compensate it from FL3, even though you will use FL1 to measure it. Hope this helps, Joe
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