The tool opens with a 180-degree protractor. Click and drag on this to move it around. Double-headed arrows appear around it when you click - click and drag on these to rotate the tool.
Click the buttons ‘Show protractor’, ‘Show ruler’ and ‘Show set square’ to show or hide these geometry tools.
You can drag shapes out of the dock at the bottom of the screen to measure them. Remove unwanted shapes by dragging them to the bin.
Clicking ‘Set up’ opens a menu where you can choose:
Clicking Reset undoes any changes you have made, returning the tool to its default state.