Earlier this week the City of San Francisco became the first public agency to pull the plug on Mac purchases after the Cupertino giant announced that it no longer wanted its computers and monitors evaluated for EPEAT certification. Now the company has carried out a U-turn and eligible products are back on EPEAT.

"We’ve recently heard from many loyal Apple customers who were disappointed to learn that we had removed our products from the EPEAT rating system" writes Bob Mansfield, Apple's senior vice president of hardware engineering. "I recognize that this was a mistake. Starting today, all eligible Apple products are back on EPEAT".

EPEAT, which stands for Electronic Product Environmental Assessment Tool, is a voluntary environmental rating that helps consumers identify greener computers and other electronic equipment. According to EPEAT’s website, it is a rating that is used by hundreds of companies, universities and government agencies in dozens of countries, and its "rigorous requirements and searchable product database let buyers bypass marketing hype and confusing specifications".

No indication is given as to why Apple removed its products from EPEAT in the first place. There was speculation that the way that Apple assembles its new "retina" display line of MacBook Pro notebooks made them ineligible for certification because the battery was glued into the case. However, these products are now in the EPEAT registry.

"If the battery is glued to the case it means you can’t recycle the case and you can’t recycle the battery," EPEAT’s CEO Robert Frisbee told The Wall Street Journal.

In the open letter, Mansfield claims that Apple is the only company that makes computers which exceed the stringent ENERGY STAR 5.2 government standard, and he believes that the IEEE 1680.1 standard -- which forms the basis of EPEAT -- would be better if it were upgraded to take this into account.

"Our relationship with EPEAT has become stronger as a result of this experience," writes Mansfield, "and we look forward to working with EPEAT as their rating system and the underlying IEEE 1680.1 standard evolve".

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