Notes:
With area selections you can measure surfaces, intensities and form features, like for example circularity.
With line selections you can measure lengths and angles
You can use point selections to count objects.
In the options-measurements menu you can select what measurements will be made.
Select redirect if your selection is in one image and you want to measure in an other image.
Use the “M” button to measure a selected region.
Results are shown in a table that can be saved and imported into a spread sheet program.