Every year Office for National Statistics (ONS) updates the UK National Accounts through a process known as annual supply and use balancing. This brings together detailed data on the three approaches to measuring gross domestic product (GDP) and balances them by product and industry. Volume series are also updated so their reference and base years are moved forward, usually (but not always) by one year. At the same time, any major methodological or classification changes may be implemented within the accounts. The publication incorporating these data is known as the Blue Book, which follows and is consistent with the Quarterly National Accounts publication.