2-At date W the site will show the value of day W bitcoin in day W dollars.
3-At other days, lets say day N, the site will show the value of (day N) bitcoin not in day N dollars, but in day W dollars.
NOPE thats not what I want.
I will try to explain with analogy.
Imagine that at january first 2020 I was 2 times faster than my brother. PS: IMPORTANT!!!!!!!!!!!!!!!!!! I didnt said what was my speed or my brother speed just how fast I was compared with him AT THAT DATE.
Now imagine that at january first 2021 I was 4 times faster than my brother. Again I said, I didnt said my brother speed or my speed at that date, just how fast I am compared with him at that date.
Can we conclude that at january first 2021 I was 2 times faster than I was at than I was at january first 2020? NOPE, because the january first 2021 information is comparing it with my brother speed at january first 2021, not with my brother speed at january first 2020 (or my speed at january first 2020).
As some example, if at january first 2021 my brother became 10 times faster than he was at january first 2020, this means I became 20 times faster [ (4 * (10*1)) / (2/1) = 20 ].
So the information I neeed at january first 2021, is not compare how fast I am compared to my brother current speed, by compared to my brother old speed , and so I will be able to find how fast I became compared to my past self.