Proportionally resizing one object to fit another object. How?

Question

Hi, thanks a lot for reading! Long time Illustrator User but I just realized I don’t know how to do something very basic. I want to resize one group of objects to fit to another object, without using pixel or cm units (all vector/relative). Here’s a short animation showing what I want to do [click first image to view animation]
As you can see, it is impossible to tell when you reached the correct spot, as it doesn’t snap to the other object when using the resize tool.

Answer 1

Thanks for the replies!
I have CS5 and Pixel Grid off and any other Grid off too.
No Emil actually confirmed that it’s simply the way the Transform Tool works, as soon as you start to drag your cursor goes its own way and leaves the starting point of the object behind. Smart Guides will not tell you when the corner you dragged from passes another point or line. The information that your cursor itself is crossing a point or line is useless. In this regard the Transform Tool is very different from the standard handles in Ai or the Transform Mode in Ps.
Ok so let’s say I go with the Transform Panel instead, is 12.853mm the exact value or does it just stop after 3 decimals and the real number is different, meaning a drag/snapping would be exact but a copy/paste of the value would be slightly off?
What if you have two objects that you want to resize together to fit a third object? For example what if I want to resize the blue and the red object to fit to the green object while staying the same size relative to each other? I could copy/paste the value for the red object but how do I then resize the blue object accordingly? What if I have a group of 10?