Instrument for measuring angles between segments in XY plane - protractor - is in the Image toolbar:

It allows you to measure the angle between two vectors, which were consistently set with the mouse on the image. Press the left mouse button to specify the beginning of the first segment, holding the mouse button draw a line segment to the end point of the first vector. Similarly, specify the second vector. Beginnings of the vectors will be shown in red, and the ends in green.

Immediately after you have built the second vector, the measured angle will be displayed on the image:

If you want to save this value to the clipboard, use functions Copy text or Add text.

Once you select a starting point for the next run, the measured values ​​will be lost.