Mr. Sikora can spend long stretches alone in the gallery, waiting for someone to enter. As soon as the first person crosses the threshold, he starts the clock, and no matter how many other people also wander in, he watches only one at a time. If someone cuts through on the way to the restrooms, it doesn't count. He records a visitor as stopping in front of a painting if both feet are planted and the person is facing the same direction for at least two seconds. He also notes details such as whether a visitor reads the label next to the work out loud.
The hardest visitors to observe, Mr. Sikora says, are the ones who drift, surveying the art from a distance, making it difficult for him to record where they stop or whether they read the painting's label. In two hours one morning, he recorded 14 observations on his computer, but discarded eight because the visitors stayed in the gallery for less than one minute, too short to count. Only one visitor qualified as what museum researchers call "a diligent visitor"—stopping at more than half the objects.