Passing variable from PHP script back to html

Hi
Testing PHP/4.2.1 and Apache 1.3.24 Win32.

No problem passing data from html to PHP script
 (<form action="breadnz_conv2miligram.php" method="post"....>
But cannot find a way to pass results from calculation made in that 
script back to HTML. 
Is there a simple way to access the variables created in the PHP script 
after the ?/ ??
did read Faq and manual but still unsuccessful!
Regards 
Henri