[dvd::rip] what is the effective ratio?

[flash@xxxxxxxxxxxxxxxxxxx]

Hi there, 

Is there any link or docs that explain the effective ratio vs physical ratio 
in the clip and zoom tab? I can't figure out how they relate and what the 
effective ratio means and does.

For example I'm ripping one movie here using the preset "autoadjust, small 
frame size, hq resize", the values I see are:

after first clipping:
dimension: 720x480
effective ratio: 1.5
physical ratio: 1.5

after zoom:
dimension: 536x402
effective ratio: 4:3
physical ratio: 1.33

after second clipping:
dimension: 496x272
effective ratio: 4:3
physical ratio: 1.82

How can the effective ratio stays the same when the physical ratio change so 
much between zoom and second clipping? And why does the efective ratio not 
change to 16:9 considering 1.82 is much closer to 16:9 (1.7777) than 4:3 
(1.3333)

I'm sure this is a beginner question, please bear with me.

Thanks,
Tim.