sentences:  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.