Period Start Date?

I am trying to better understand my cycle. At the beginning of this cycle I knew my period was coming when I got some slight bloody discharge on my finger when checking for cervical mucus. The next day was the same thing… Only noticed some blood when checking for cervical mucus.. by following day if there was enough blood that I needed a pad or a tampon.

Do I count the start of my cycle as Friday (the first day that I noticed blood when I noticed blood when I was looking for cervical mucus) Or do I count it as Sunday (the first day that I needed a tampon)?