Karlin also determined "the optimal length for a phone cord":
Telephone company executives wondered whether the standard cord, then about three feet long, might be shortened. Mr. Karlin’s staff stole into colleagues’ offices every three days and covertly shortened their phone cords, an inch at time. No one noticed, they found, until the cords had lost an entire foot.Despite these efforts at helping, he found himself referred to as "the most hated man in America," because his name was attached to the decision — made in the 1960s — to switch to all-digit phone numbers instead of things like PEnnsylvania 6-5000." The phone system was running out of numbers made from pronounceable words, and it was Karlin figured out that people would be able to remember 7 digits.
From then on, phones came with shorter cords.
Mr. Karlin also introduced the white dot inside each finger hole that was a fixture of rotary phones in later years. After the phone was redesigned at midcentury, with the letters and numbers moved outside the finger holes, users, to AT&T’s bewilderment, could no longer dial as quickly.
With blank space at the center of the holes, Mr. Karlin found, callers no longer had a target at which to aim their fingers. The dot restored the speed.
I'm old enough to have lived through the big switch from named "exchanges" to all numbers. There was a lot of anguish, back then, over whether the human individual was being turned into a number. It was also in the 60s — 1963 to be exact — that the post office forced ZIP codes on us. Before then, you had a number in between the city and the state names. I remember the last line of my address being Wilmington 3, Delaware. The government tried to soothe us by personifying the number as a human character, Mr. ZIP:
It's hard to imagine the government today using such an obvious, laughable technique as it pushes us into a life of regimentation. Mockery would be made. But those were simpler times.