The RCCB which covers a few MCBs? There is usually a sticky label pack in with the CU which shows which ways the RCCB covers, usually green for RCD protected ways and red for non RCD protected ways. If you have more than one RCCB then can also label the section of MCBs up as "A circuits", "B circuits", "C circuits" noting on each RCCB which set it feeds, if you can make it out on here: http://www.tlc-direct.co.uk/Images/Products/size_3/WYNHRS10SSLHI.JPG