I often use a digital watch while exercising. In my dream I used it to obtain lucidity. When I looked it was a reasonable time (3 in the afternoon) however for every second after that the digits in the time, date, and second areas would change to random numbers. Also, the number of digits would not always fit the category (such as 5645 seconds). I think that it's amazing that I imagined a new set of random digits every second (or what I perceived as a second) without even consciously thinking about it! I then switched the watch to stopwatch mode and surprisingly it worked! At 5 seconds I looked away from the watch for a few seconds and looked back and it showed 8 seconds which seemed just right. I then continued to stare at the watch until it reached 40 seconds. At that point I lost my lucid rationality and continued with my dream, believing that I could see how long my dream lasted by checking the real stopwatch after I woke up.

I've only had one other lucid dream where I was aware enough to test how things work in a dream, but I really hope I have more because it's really fascinating!