It's just math: numbers through an equation
The data in the orange part of the parabola
generate the parabola projection (blue).
There are usually multiple parabolas for a trend.
The calendars are precise.
Data is collected daily and every 30 minutes.

  First time users be sure to try out the SP 30 min   Slideshow.  And the History Thumbnails

  Updated weekdays by 8 pm CST

  More Description?