Flush input device

Hi, I am trying to implement a double tap using the keyboard device and I have set the slide object to accept 2 responses, and used an inline to branch what happens if the 2 responses (of the same key) happen within a specified time frame. Specifically, If time between key presses < 500 ms, proceed to next slide Or else go back to Label at the beginning of the slide. * I am having some trouble in that when the two key presses are indeed less than 500ms apart, the screen progressed to the next slide but when the presses are more than 500ms apart, future double taps (two key presses less than 500ms apart) are not effective. I am guessing this is because any response after the 2nd response is taken as the 3rd (and more response). How do I configure the inline such that if the first 2 key presses are not made within a maximum 500ms time frame, they are flushed (cleared) from memory and the following response is considered as the first response again? Thanks