DPlot finds the area under a curve using the trapezoidal rule:
Typical uses for integration include generating an impulsetime history from a pressuretime record, or velocitytime from accelerationtime.
For polar charts, DPlot uses
(x in radians)
For a circle this will give an integrated value of (approximately, depending on the spacing between points) πr2 at x=360 degrees, as expected.
Shortcut:
Click on the toolbar. 

Related macro commands 
Page url:
https://www.dplot.com/help/index.htm?helpid_integrate.htm