The market value (now) is calculated based on your current cryptocurrency holdings tracked by CoinTracker. This is the sum of the current balance on all your wallets & exchanges + any manual transactions.
If you change the date on the performance to chart (including today’s date), the computation changes to be based on your transaction history (e.g. the sum of all transactions synced on CoinTracker). If your complete trading history (e.g. all fiat → crypto → crypto → fiat transactions across all exchanges and wallets) is not tracked by CoinTracker (or if there are any extraneous or missing transactions) then these will not match. In order to fix this, please follow these steps.