The percentage change on the portfolio history graph is actually not the profit! This is just the balance change.
The portfolio history graph is a graph of the 'total portfolio worth' and gives you the changes in your total portfolio value over time. Thus new purchases or fiat deposits also show as a change here, since they are changes in your portfolio's worth. The all-time value shown here is the increase in your portfolio worth since the beginning and not the profit.
For all-time profit, refer to the portfolio main screen as shown below:
PRO TIP: If you want to find out what other numbers in your portfolio mean, you can follow this guide here.
PRO TIP 2: We are working on improving the portfolio analytics page in Delta so it might look a little different by the time you read this.