This is another great way of adding linear dimensions to your drawing and is most frequently seen in drawings that contain lots of features, such as a sheet metal part containing many grooves and punches. To use this dimensioning tool, we will first move point A of our example drawing to the origin. When we are done adding the ordinate dimensioning, you will understand the significance of moving point A to the origin:

1. To move the drawing so that point A goes to the origin, select the Move tool from the Modify panel, then select the entire drawing and press the Enter key.
2. Now click on point A to select it as a base point and then type 0,0 and press Enter again.
3. The drawing will now move so that point A overlaps the origin.

Now we are ready to add the ordinate dimension to our drawing and in the following example, we will learn how to do just that:

1. Click on the Ordinate tool from the Dimension drop-down menu and click on point A.
2. Move your cursor below line A and click again to place the dimension. You will notice that the dimension value now displays 0, which is basically the X coordinate value of point A.
3. Select the Ordinate tool again and click on point B and again move the cursor below line AB and click again. This time, you will get the value of the cursor too, which is basically the X coordinate value of point B.
4. Similarly, add the ordinate dimension values to points D and F. The final dimensioning should look like the following screenshot: 

So, in this case, the dimensions are showing the X coordinate value of the selected point and since we have moved the first point, A, to the origin, the respective distances are measured with respect to point A. So, at point B, we have the distance between point A and B, and at point D, we have the distance between point A and D. Similarly, at point F, we have the distance between point A and F. So, essentially, using ordinate dimensioning we are adding dimensions with respect to the origin. This method of adding dimensions is cleaner than simple linear dimensions as you don't need the start and end points for every dimension.

We can also add a vertical ordinate dimension, and in that case, the distances will also be measured in the vertical direction with respect to the origin, or in this case, point A. The ordinate value will be the Y coordinate value of the selected point in the vertical direction:

In my case, the vertical and horizontal ordinate dimensions looked like the preceding screenshot. Here, all the distances of points L, K, and I are measured with respect to point A, or the origin.