identity. This was a considerable innovation in British exchanges since in Strowger exchanges the directory and equipment numbers had to be the same. The switching in TXE2s was carried out by reed relays and a typical TXE2 contained about 100,000 reeds. The reeds were fast in operation, with a life expectancy of more than 10 million operations. The glass capsules were about an inch (25 mm) in length and about an eighth of an inch (3 mm) in diameter. Four reeds were generally present inside each relay coil, two for the speech-path, one for holding the path and one for metering. Switching with these reeds held out the prospect of much greater reliability compared with the Strowger system, where switching was carried out by base metal wipers moving through banks of metal contacts. The Strowger switches required routines to be carried out on them to clean the banks: they also required oiling and occasional adjustment. Reed relays required none of this. However, in practice, and particularly in the early years of the system's service, the performance of the reeds proved to be worse than had been expected. Maintenance and reliability The TXE2-specific equipment was different in the TXE2s manufactured by Plessey, STC and GEC, so that spare equipment had to be held for each type of manufacturer. Importantly, each manufacturer made their own reed inserts (reed were manufactured for GEC by their subsidiary, the Mazda Osram Valve Company) and their performance differed significantly in the first years of production. All the TXE2-specific equipment was mounted on slide-in units, mainly single-width, but some double-width. There was a structured holding of maintenance spare units. For those which were likely to be needed frequently or urgently in every exchange, such as a Subscribers Line Unit, a spare unit was held in every exchange. For those units for which a spare was likely to be needed less frequently or urgently, the spares were held at an Area centre serving perhaps 6–10 TXE2s of the same manufacture. Finally for those units for which a spare was likely to be needed seldom, the spare units were held at one centre per Region - there being ten Regions in the UK. In the early (around 1969) Plessey exchanges, a significantly high proportion of the reed-inserts were contaminated with a high-resistance film and were prone to giving an intermittently high-resistance contact. If this occurred in one of the