The History view allows you to visualise bandwidth activity of any of your targets, up to years in the past, if you have the data.

You can access the History view by either clicking the  button in the toolbar above the graph, or (if the graph is now showing), right-clicking the Target area and choosing History...

Viewing data points / details

The History graph supports mousing over individual points to see the actual values. You can also drag-select a range of values to see either a total or aggregate (average) for that period.

The Toolbar

The toolbar along the top of the History window controls the period of time being shown in the graph, as well as what sort of information is shown (usage or speed), how it is displays (combined or split) and the level-of-detail.

From left to right, the controls are:

PeriodThis dropdown controls the period for which to display data. There are a number of preset periods, or you can select Choose Dates... and choose a start and end date.
RefreshForces a refresh of the graph. Note normally this isn't required; the graph will auto-refresh every minute or so. There are some circumstances where this will not happen however: if the graph takes a long time to render, auto-refresh will be automatically disabled to prevent excessive CPU utilisation. If you're finding the graph isn't automatically refreshing, try dropping the level of detail or the time period to speed up rendering and re-enable auto-refresh.
ShareBrings up the Sharing menu allows you to export a picture of the graph via Email, iMessage, Airdrop etc.
Usage / SpeedThis toggles whether each point on the graph shows the total amount of data used (usage) or the average speed for that period (speed). Usage is always shown as a bar chart whilst speed is always shown as an area chart.
Combined / SplitDetermines whether to show inbound and outbound graphs on the same axis or split them onto separate axes.
Level-of-detailThis controls how much time each point on the graph represents. For example, if you're viewing 12 hours of data you're likely going to want to see the data in 5 minute intervals. If however you're viewing several months of data, you're likely going to want to see the data in one-day intervals. Note that viewing higher levels of detail for longer periods may require a few seconds to calculate.