Proportional Scale, Single Axis Scale.Proportional scale
It allows you to modify the size of the current object. It expands or shrinks the object in all the directions at the same time.
You can choose a fixed point which will be the origin (reference point) of the size modification. By default, this point is the base of the model. Hold the option key, and click (Mac) or click the right mouse button (Windows), and you will get an X (cross) cursor. Now click on a different location (with the left mouse button if using Windows) to set the fixed reference point. Here, I have set it near the top of the sphere.
After applying the scale again, the sphere has been expanded toward the bottom (away from the reference point at the top)
Single axis scale
This modifies the size of the current object. It expands or shrinks in one direction only, from the base of the model, or another point if you've changed the fixed reference point. To change the axis, depress the space bar until you get the axis you want. You can use the tab key to enter a numeric value for the amount of scale to apply.
To change the fixed point which will be the origin of the size modification, hold the option key, and click (Mac) or click the right mouse button (Windows), so you will get an X cursor. Click on a different location to set the fixed reference point.
In the example below, the fixed reference point is still at the bottom but since the scale is done along the horizontal axis the sphere turns into an oblong ellipsoid.
