[agentxi]

i'm not sure exactly what you mean, but i will pretend I will, and explain something...and hope it's the right information.

to constrain a circle (this also works with rectangles as well or any transform tool/scaling)

UNIFORM SCALING, PERFECT CIRCLE , SQUARE:
hold shift while creating it, it will scale the x and y values the same at the same time.
SCALING FROM CENTER, CREATE CIRCLE OR RECTANGLE FROM POINT OF CLICK:
now to create a circle/rectangle/scaling from the center of the click or already exsisting object (if you're scaling an object) you hold down alt.

USING BOTH OF DISCUSSED PROCEDURES TOGETHER:
now if you want to create a perfect circle, square or uniform scale, from the center, then you hold down both shift and alt, while you do it.


wow, now i feel confused, I hope it reads right (i'm tired)

~agentxi~