Although whole code wheels could not be directly photocopied, the component wheels could be disassembled and individually photocopied; these components could then be crafted together into a duplicate wheel. The contents of code wheels could also be copied onto paper and the user of an unlicensed copy could simply apply a mathematical formula to the presented challenges to calculate the correct response. Once a suitable formula was found, code wheels actually made the process of copying easier since the amount of information they could contain was low compared to a manual of potentially unlimited size. Thus, code wheels were rapidly phased out in favor of regular manual protection and protection based around color, as public access to color photocopying at the time was expensive and uncommon. This was itself made obsolete by a return to protection based on the game media itself, when CD-ROMs were introduced.