You can easely measure the distance between two points of an image with the linear, you can write down the data into the clipboard using Copy text and Add text commands. But if you want to mesure not only distance, but also height difference between the same points, use Measure distance and height function.

Select a segment with the linear and call the function Edit → Measure distance and height. Calculated values will be added to the clipboard and the final point of the segment will be marked. It is convenient to use hot key combination Ctrl+D to call this function.

When you have finished with the measurements, paste the data table from the clipboard to Microsoft Excel or any other program for statistical analysis