It is possible to acquire data with BD FACS Diva ratiometrically, meaning one parameter is divided by another such as FL1/FL2, to create a new parameter representing these values. The resulting ratio parameter will be stored as a new parameter with the .FCS file and this parameter is dynamically calculated in BD FACS Diva through the use of a special keyword that is stored in the header.
To display the ratio in FCS Express you must complete a few simple steps to construct a parameter math formula to either use the FACS Diva method for creating the parameter or the FCS Express method. The benefit of using the FCS Express Version 4 method to calculate the ratiometric data is that unlike BD FACS Diva the new parameter can use the actual ratio value rather than a value created by using a multiplier. If you would like to create a new ratio parameter using the FCS Express method please see the Using Parameter Math topic for details on creating a simple ratio parameter.
Recreating a ratio parameter from BD FACS Diva data:
1. Insert and select any plot of the data you wish to recreate the parameter for.
2. Click on the Data Tab>Calculate>Parameter Math>Single Calculation.
3. Enter a name for the new ratio parameter in the Output Parameter Name box.
4. Click on the Formula radio button.
5. Enter the following formula where X is the parameter number of the numerator parameter and Y is the parameter number of the denominator parameter:
=(pX/pY)*
6. Right click next to * symbol.
7. Choose Insert Token from the drop down menu.
8. Choose Keyword in the Insert a Token dialog
9. Choose the Keyword category.
10. Enter the keyword PXSF where X is the parameter number of the ratio parameter stored by BD FACS Diva. In the example below the keyword parameter number was 6.
11. Click OK.
12. Click Calculate.
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You can now click on the axis of your plot to access the newly created ratio parameter which will look as it did in BD FACS Diva.
The parameter math can also be defined as Parameter Math Sequence which will automatically apply the calculations upon opening new plots using the same formuals above. Please see our Parameter Math section in the FCS Express manual for details on setting up a parameter math sequence.