I'm programming an application to measure time intervals. The application contains several timers on one screen. Only one of these timers can run at once. My initial design has a start button and a stop button for each timer. When the user starts the timer with start the stop button is greyed out and when the timer is running the start button is greyed out.
Question: would it be better to have rather just one button, which would display either the text "stop" or "start" depending on whether the timer is running or not? I'm a bit torn on this issue, as I consider it an advantage when the user sees all the available options at once. On the other hand, having just one button would provide a cleaner design.