Base point

Base point is the center about which the size is changing when you use parameteres rollout. You can adjust its position at any time using the Base point sub-object level. The 3x3 lattice will appear and all you need is to select the new lattice point and the Base point will move there. After that all size changes will be made respectively to the new point:

Pivot to base

This option allows to move object Pivot point to the place where Base point is located