appearing size of shapes

[Denny Beyer <denny esru strath ac uk>]

hey dia list members,

i posted this question befor, but no one answered really and i can't 
work it out myself. Sorry for inconvinience!
The question is: on what depends the size of an included shape. It 
happens, that my own created shapes appear in very different sizes on 
including them.
How can i make them appearing in one size, lets say 1 x 1 (eg. in cm, 
according to rulers)?

Thanks for your help,
denny