This line chart displays the historical value of your portfolio in a given currency, over a given period, compared to the initial converted value of your portfolio in that currency.
The resolution of this chart is daily.
This chart does not consider activities such as withdrawals or deposits when calculating the profit/loss ratio. This functionality will be supported in the future.
If you are looking for the actual converted value of your portfolio, consider the Converted Value chart.
For each account, address and offset in your portfolio, the balances, history and transactions are summed up for each currency, and converted with the closing (composite) rate for each day; this value is then divided by the earliest converted value for your portfolio, to give a profit/loss as a ratio/percentage.