Mr. Tesler, who worked for several leading tech companies, including Xerox, Apple, Amazon and Yahoo, devoted much of his career to the idea of making computers practical, affordable and easy to use.
During the 1970s, he worked at Xerox’s Palo Alto Research Center in California, which produced many breakthroughs in computer technology. Among other advances, Mr. Tesler was credited with helping develop the terms “user-friendly” and “WYSIWYG,” for “what you see is what you get,” to describe the goal of having computer printouts be the exact duplicate of what is seen on a screen.
He also devised what is known as Tesler’s Law, a tenet holding that, in any computing system, there is a level of technical complexity that cannot be reduced.
It was Mr. Tesler’s work on the Gypsy word processor at PARC during the 1970s that turned out to have the greatest utility and long-term impact. With his interest in simplicity and ease of use, he sought ways to make computers more interactive for consumers, a notion called “user interface” in computer design. In developing his designs and ideas, Mr. Tesler often asked ordinary users — rather than computer experts — what they wanted their machines to do.
At the time, computers operated in separate “modes”: For instance, text could be entered in one digital mode, but for editorial changes to that text, the user would have to switch the computer to a different mode. Mr. Tesler helped refine the concept of “modeless” computing, in which a user could perform a variety of functions at all times without manually changing how the computer would operate.
For his best-known innovation, Mr. Tesler adapted an age-old practice of schoolchildren — cutting out pictures and pasting them in scrapbooks — to computers. At first, he thought cut and paste would apply strictly to design and visual images.
“I would have some analogous thing called delete and insert to use for moving text around, but it would have the same concept,” he said in a 2013 oral history interview with the Computer History Museum in Mountain View, Calif. “After a while, I thought you don’t really need a different name. We can probably teach people what cut and paste means even if they’ve never heard of it before.”
Mr. Tesler and another computer scientist, Tim Mott, “did user testing at every stage of the development. He was the one that came up with the idea of the double click to select a word.”
While attempting to find the easiest way to copy a word or line of text, Mr. Tesler recalled, “one day Tim came in and said, ‘Last night I just was tapping on the table and went tap, tap, tap, tap. How about tap, tap? That would select a word.”
By pressing or clicking on a computer mouse and then dragging the cursor across an image or a block of text, the selected material could be highlighted, or cut. A similar procedure with the mouse would allow that text to be copied or pasted onto another part of the computer document on the screen.
The technical advance was not put into widespread practice until years later, after Mr. Tesler had left Xerox for Apple. Cut-copy-paste was incorporated into Apple’s Lisa computer in 1983, then became a standard function on the Macintosh operating system, which was introduced a year later. It is now an essential element of every digital device.
Mr. Tesler even developed a way to make the action of the mouse more precise by developing “a software algorithm that controlled for hand shake as you were dragging the mouse,” he said in the oral history. “As long as they’re starting out with a horizontal motion, we . . . assume [there will] be some shaking in the vertical direction and kind of ignore it unless they go all the way into the next line, like more than halfway into the next line. And then go, ‘Uhm . . . they really do want to go to this line.’ ”
Lawrence Gordon Tesler was born April 24, 1945, in the Bronx. His father was a physician, his mother a homemaker.
Mr. Tesler became fascinated with the emerging technology of computers in the 1950s, when he saw computers used to predict presidential elections. He studied mathematics at Stanford University, where he did computer programming for medical researcher and Nobel laureate Joshua Lederberg. After graduating in 1965, Mr. Tesler became a computer programmer and worked at the Stanford Artificial Intelligence Laboratory.
He joined Xerox in 1973 and reportedly demonstrated the company’s Alto computer to Steve Jobs, who later adapted the Alto’s mouse and other elements to improve the design of the personal computer. Mr. Tesler followed Jobs to Apple in 1980 and held various high-level positions at the company, including chief scientist — a job once held by computer visionary Steve Wozniak.
After leaving Apple in 1997, Mr. Tesler founded a software company and later worked at Yahoo and Amazon, where he was vice president of “shopping experience” and worked on Amazon’s program allowing customers to preview books online.
Survivors include his wife, Colleen Barton of Portola Valley; a daughter from an early marriage that ended in divorce; and two brothers.
Always interested in software and design, Mr. Tesler worked on many elements of computers now taken for granted, such as the proper tension in the cord attached to a computer mouse and the amount of finger pressure needed to click the mouse.
In the Computer History Museum interview, he recalled a discussion about the computer mouse with a design engineer.
“This button is going to be pushed a lot and people are going — their hands are going to tire if it’s too stiff,” Mr. Tesler said. “And the button is going to wear out. He said, ‘Oh, don’t worry about it. This button is rated for 40,000 presses.’ . . . And so we did a little calculation on the back of a napkin and I said, you know, ‘Ten button presses a minute and so and so an hour, eight-hour day, you know, 3 million button presses,’ or something like that. He said, ‘Oh. People aren’t going to press it 10 times a minute.’ . . .
“I said, ‘Have you ever seen anybody use a mouse on a computer?’ ”
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