In the United Kingdom, the first Director exchange in London, Holborn Tandem, was cutover in 1927; preceded by any necessary changes in the London area, e.g. changing some exchange names and making all local numbers (4N) 4-digit. As each digit represents three letters the same network cannot have exchanges called BRIxton and CRIcklewood, which both correspond to 274. In smaller director areas some A-digit levels were combined so that local director exchange would only need four or fewer groups of directors instead of eight. But if (say) A-digit levels 7 and 8 were combined it would not be possible to have both PERivale and TERminus exchanges in the same network.