How to change dimensions of an object proportionally? I need to change the 3 dimensions of an object, but only by changing one dimension.

That is, if the object has the following dimensions:  


height: 2 units (Z)
width: 0.5 units (Y)
depth: 0.1 units (X)


When I change the height of 2 units to 3 units, then the other width dimensions (Y) and depth (X) should automatically change to 0.75 and 0.15 respectively.

I do this by scaling (S):


I press the S key 
I press the = key
After Income Division 3/2. 3 is the new dimension and 2 above.


But I would like to know if there is a better way to do so through the properties panel (N).
The options in the properties panel, when I change the height of 2 units to 3 units, the width and depth do not change.
There is a solution since version 2.70:
http://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.70/UI#Multi-Number_Button_Editing

Click and drag from the first to the last fields you want to edit and release the click. The three fields are highlighted. Enter an expression, eg. *3/2 and press enter. All fields are edited at the same time.