First, set "Center date of timeline." 1800 seems like a good place to center the timeline, so we'll enter ". According to the Visualization Index, however, this field should be in the DD/MM/YYYY format. We'll pick an arbitrary date and enter "01/01/1800" in the field. If you want to set a specific day, you would use the month/day/year format ("01/25/1800"). | 
