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You may request scans from multiple journals and books. But, under the terms of the Copyright Licensing Agency, we are usually only allowed to digitise for a given module one article from any individual journal, one chapter from any individual book, or up to 10% of the whole book (whichever is greater).
It is advisable that you add the record of the item you wish to digitise to your reading list beforehand, if you are not sure how to do that, look at the section "Add Items".