To characterize the perceptible performance of interactive applications, we measure the response time of user requests (episodes) by instrumenting the Java GUI toolkit's event dispatch code. The instrumentation measures the wall clock time it took the application to handle the request. As research in human computer interaction has found, requests that are shorter than a given threshold (around 100 ms [5]) are not perceptible by the user. Requests longer than 100 ms are perceptible and can negatively aect user satisfaction and productivity.