Same as uptime, volatility is available under the statistics tab in the diagnostic and is calculated from your global statistics data. It takes into consideration all data points with online status and is calculated as the ratio between standard deviation and average daily profitability. This measurement tells you how much the estimated daily profitability fluctuated in one day in percentages. The more the data fluctuates, the less reliable the currently observed daily earnings estimation is.
There isn't much to do to improve the volatility of your daily earnings except observing the data market and maybe changing the coin you are currently mining. If you are using an auto-exchange pool or a marketplace and the volatility is not in the acceptable levels, then you might also consider switching to direct coin mining.
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