1
I am reading Bitcoin wiki and it says
over the previous 2016 blocks. Can be further simplified to
D * 2**32 / 600without much loss of accuracy.
I guess the reason of reducing to 2**32 is for computing convenience (bit operation). However, 0xffffff / 2016 = 32.507440476190474 and 0xffffff / 2048 = 31.99951171875 which is more accurate.
Why was 2016 chosen instead of 2048?
1
2016 blocks at an expected interval of 10 minutes are exactly 14 days. Likely the window for the difficulty period and interval were picked first and 2016 resulted from that.
0
For calculating the difficulty retargeting, the equation is:
New Difficulty = Old Difficulty * (Actual Time of Last 2015 Blocks / 20160 minutes)
20,160 minutes is two weeks based upon a desired 10-minute block time; hence the 2016 blocks.
P.S. I actually do mean 2015 blocks. Even though the retargeting itself happens every 2016 blocks, due to an off-by-one error in the original Bitcoin Core client (my bad ;)) it is based on the total time of the previous 2015 blocks only.
