Did you know that hidden in the Speeds option of the data display, you get a table which not only shows your IAS [Indicated Air Speed] and TAS [True Air Speed], but also shows a GS [Ground Speed] indicator as well. Both in knots and mph.
In the Settings –> Data Output screen, you can also click the Disk (data.txt file) checkbox and a series of speeds gets written to a txt file. You can even set the time increment between each recorded data point.
Here’s a link to a useful Wikipedia article explaining what airspeed actually is: