Timer sensors trigger their callback function at regular intervals. For example, a timer might be setup to call its callback function every second on the second by setting the base time to SbTime(0.0) and the interval to SbTime(1.0). Timers are guaranteed to be triggered only once when the timer queue is processed, so if the application only processes the timer queue once every 5 seconds (because it is busy doing something else) the once-a-second sensor's callback will be called only once every 5 seconds.

Note also that SoTimers always schedule themselves to be triggered the next even multiple of the interval time after the base time; so, for example, if the once-a-second sensor is triggered at time 2.9 (because the application way busy doing something at time 2.0 and didn't get around to processing the sensor queue for a while) it will reschedule itself to go off at time 3.0, not at time 3.9. If the base time was never set, the sensor would be scheduled for time 3.9.