This is a linked open data (LOD) about date and time. "C.E. 1806 February 28" is a date of Julian/Gregorian Calendar (reformed in 1752) (Calendar ID: 101.2).
http://datetime.hutime.org/calendar/101.2/date/C.E._1806_February_28
hcal:101.2/date/2380745.5
hcal:101.2/date/C.E._1806_February_28
hcaldate:2380745.5
hcaldate:C.E._1806_February_28