Make a Spiral:

There will be a picture here:  I will stop using jpeg assuming we will have it built in.
<imagettp: GROWBY 20% 8 [FD 50 RT 90]>

To make this picture in SeeLogo type FD 50 RT 90
then type GROWBY 20% 8 IT and you will see the picture.

Now look at the editor and see the numbers 20% 8.  What do you think will happen if you change them?  What do you think they mean?