Week 2: Where the thresholds came from

Why interface guidance has three numbers in it, who measured them, and what they were measuring at the time.

23 February 2027

The thresholds that decide whether a delay gets no feedback, a spinner or a progress bar were not derived from a theory of attention. They came out of terminal sessions in 1968 and a usability textbook in 1993, and they have been copied forward ever since.

This lecture traces the numbers back to what was in front of the people who measured them. That matters, because a threshold written for a mainframe terminal is still deciding what your software does when a request is slow.