Historical data - hmm, we're saving data daily, but it's not available online, only by request. I can get it for you if you need, just ask. It will be daily per-minute CSVs, but it's not going to long in the past, as we've started tracking global averages not so long ago.
Ah, that's way more detail than I want. Ok, let me take a step back and explain what I'm really looking for...
I would like to see a daily indicative Bitcoin price for each calendar day (ideally both published on the web site and accessible by an API). There is often a need to determine the market value of an asset for tax or accounting purposes. For pragmatic reasons, in many circumstances it is adequate to calculate the market value using an indicative price for the asset on the day in question; for shares, published daily closing prices are often used for this purpose.
Currently the only published indicative daily prices for Bitcoin are Coindesk's published 'closing prices' for their Bitcoin Price Index. I don't find their methodology ideal for a number of reasons, but that's a separate discussion. For now, what I'd like to see is more providers publishing such pricing data.
I don't have a strong feeling how the daily price index should be calculated. Volume-weighted average over the day? Midprice at a particular time of day? (Noon? End-of-day? i.e. midnight.) Nor do I have a strong feeling for what timezone is used to define 'day'.
It would be great to have more options for getting data like this than Coindesk's current data...
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