The paper by Robert B. Miller from IBM explores the concept of response time in man-computer transactions, addressing the controversy surrounding the acceptable response times for user commands or inquiries. The author identifies two major semantic issues: "Response time to what?" and "What is a need or requirement?" He argues that different human purposes and actions have different acceptable response times, and that a two-second response is not universally required. The paper categorizes human actions and purposes into various classes and discusses the impact of response times on operating and psychological needs. Operating needs, such as the need for an airplane to exceed stall speed, are contrasted with psychological needs, which include the need for timely responses to expectations and the need for psychological closure in tasks. The author emphasizes the importance of response times in maintaining continuity of thought processes, particularly in complex problem-solving. He suggests that response delays greater than two seconds can lead to sudden drops in mental efficiency, creating psychological step-down discontinuities. The paper also discusses the impact of response times on user confidence and the need for system design to minimize interruptions and delays. The paper provides detailed estimates of acceptable response times for various types of user interactions, including control activation, system availability checks, complex inquiries, and graphic manipulations. It highlights the importance of user experience and the need for systems to be designed with short response times to maintain user engagement and productivity. Finally, the paper addresses the discontinuity of waiting time at 15 seconds and the importance of quick recovery from errors and failures to minimize user demoralization and maintain motivation. The author concludes by emphasizing the need for systems to be designed with short response times to ensure effective and efficient human-computer interactions.The paper by Robert B. Miller from IBM explores the concept of response time in man-computer transactions, addressing the controversy surrounding the acceptable response times for user commands or inquiries. The author identifies two major semantic issues: "Response time to what?" and "What is a need or requirement?" He argues that different human purposes and actions have different acceptable response times, and that a two-second response is not universally required. The paper categorizes human actions and purposes into various classes and discusses the impact of response times on operating and psychological needs. Operating needs, such as the need for an airplane to exceed stall speed, are contrasted with psychological needs, which include the need for timely responses to expectations and the need for psychological closure in tasks. The author emphasizes the importance of response times in maintaining continuity of thought processes, particularly in complex problem-solving. He suggests that response delays greater than two seconds can lead to sudden drops in mental efficiency, creating psychological step-down discontinuities. The paper also discusses the impact of response times on user confidence and the need for system design to minimize interruptions and delays. The paper provides detailed estimates of acceptable response times for various types of user interactions, including control activation, system availability checks, complex inquiries, and graphic manipulations. It highlights the importance of user experience and the need for systems to be designed with short response times to maintain user engagement and productivity. Finally, the paper addresses the discontinuity of waiting time at 15 seconds and the importance of quick recovery from errors and failures to minimize user demoralization and maintain motivation. The author concludes by emphasizing the need for systems to be designed with short response times to ensure effective and efficient human-computer interactions.