Source: Coinbase  

Release: Coinbase Index  

Units:  Index Jan 1, 2015=100, Not Seasonally Adjusted

Frequency:  Daily, 7-Day

All data is as of 5 PM PST.
Given the volatility in the cryptocurrency markets, users may wish to view the large variation in values in a log scale. Changes in the data can be analyzed by turning on a log scale functionality that can be applied in the Format tab under Edit Graph button.
For more information to the Coinbase index, see https://am.coinbase.com/index

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Reproduction of Coinbase data in any form is prohibited except with the prior written permission of Coinbase.