Bitcoin vs US Equities Correlation

How to read this chart

A correlation statistic is used to determine whether two things are positively correlated (they both go up), uncorrelated (they trade independently of each other), or negatively correlated (one goes up, the other goes down). 

A value closer to plus 1 represents a positive correlation, closer to 0 means they are uncorrelated, and as numbers approach minus 1, assets are negatively correlated.