The base game provides a 24-hour price history for all instruments.
This DLC allows you to extend this feature to cover the last 7 days.

The extended price history for each instrument is dynamically loaded
based on the charts you are viewing. Data for the past 7 days will
automatically populate if over 10% of the chart remains undisplayed,
or if you've opted for a longer timeframe (15, 30, or 60 minutes).

To access this extended 7-day price history, make sure the DLC is
enabled in your Steam client. A calendar icon (📅) in the game's
window title indicates that the feature is enabled and ready to use.