The Linear dimension tool will add horizontal or vertical linear dimensions only. So, the very first dimension that we added here was a horizontal one from point A to B. Now, select the Linear dimension tool again and then click on point H and then on point G and move your cursor away from line HG toward the right and you will notice that now we are adding a vertical dimension, as in the following screenshot:

Line HG is inclined to an angle, still the linear tool will only create the dimension that is either horizontal or vertical and the type of dimension, that is, horizontal or vertical, that you will get in this case will depend on the point where you put it. So, instead of moving toward the right, if you move your cursor in a downward or upward direction after selecting points G and H, a horizontal dimension will be created.