The use of letters on dials was proposed in 1917 by W. G. Blauvelt of AT&T. Large cities like New York would ultimately require a seven-digit number, but some tests in the early 1900s indicated that the short-term memory span of many people could not handle seven digits and many dialling errors due to memory lapse might occur (the documentation for these tests is lost). Hence the first Panel automatic exchanges cutover in 1915 in Newark, New Jersey used "semiautomatic" operation with the local operator keying the number for the caller. And as large cities would have both manual and automatic exchanges for some years, the numbers for manual or automatic exchanges would have the same format (originally MULberry 3456, with three letters then four numbers), which could be either spoken or dialled.