How can I create a patch between a tag and the HEAD of a branch in CVS?

Question

I have the following script but it looks like is comparing the tag with Head instead of the Branch:

@echo off
cd outlook
SET /P startTag=Enter the start tag name to be compared with current HEAD
SET /P branch=Enter the branch name to be used in comparison
cvs patch -kk -R -r %startTag% -D now outlook> ../%startTag%.patch
cd ../

What do I need to change so it actually compare HEAD of the Branch?