Quick AF question....

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Ok, this may sound stupid.  I'm just curious on the glow app what actually constitutes as your first day of your AF?  On some other apps it's the day you see red blood and others it's the first day you see spotting.  Which one is the best to use?  
​FYI been trying for a few months and want to make sure I have this right.  Thank you!!!!  
Baby dust to all ;)