Measuring points are orthogonal by default. To allow measurement between two points that are diagonal, hold the SHIFT key while dragging the mouse.
Whenever a measurement point is set to a wall, it will snap to the wall with some offset distance. To prevent snapping to a wall, press the CONTROL key.
To terminate the current measurement operation, press the ESCAPE key. Once terminated, measurement information, including measurement line and measurement label is removed from the scene.
Switching to another operation would also terminate the current measurement operation.