modify scale?

[DRMRLPLS]

There must be some silly key modifeir for this but I can't find it:

when in modify scale mode if you pull on one of the side(not corner) handles, 

sometimes it pulls only to that side, and sometimes it grows from both 

sides(as if centered), what does this depend on?  SOmetimes I want the left 

side to remain anchored and to only pull the right side.  I must be missing 

somethig very basic, but it's driving me nuts. :-)  any suggestions?


Andrew