$WBFUP - bytes uploaded
$WBFUP is available for use with all WBSP
FULID - server-side generated unique form upload ID
generated using WB_FULID variable and retrieved with $WBFULID tag.
Number of bytes that already have been uploaded by form
identified with FULID.
Here's an example:
After running this example
(together with upload.wbsp file that can be found here), WhizBase will display the upload