Late in 1936, an MIT professor named Robert Elder presented a new invention at a conference held in the ballroom of the Yale Club of New York. He called it the “Audimeter” and claimed that it could scientifically measure human attention, something no one had done before. The crude prototype had two rolls of paper in a reel-to-reel arrangement and was attached to a radio. When the radio was on, a stylus scratched a line onto the slowly turning scroll, indicating over time which stations the radio had been tuned to, and for how long.

Tim Wu, The Attention Merchants, loc. 362