Why is there a discrepancy between the 1,260 days of Rev. 11:2-3) and the 1290 days of Daniel 12:11?

Revelation 11 New International Version (NIV)
The Two Witnesses
11 I was given a reed like a measuring rod and was told, “Go and measure the temple of God and the altar, with its worshipers. 2 But exclude the outer court; do not measure it, because it has been given to the Gentiles. They will trample on the holy city for 42 months. 3 And I will appoint my two witnesses, and they will prophesy for 1,260 days, clothed in sackcloth.” 

Clarify • Share • Report • Asked December 07 2019 • Jack Gutknecht