PDAs have emerged as the saving grace for psychologists who study people\u2019s moods.Since the 1940s, researchers conducting so-called diary studies have asked participants to record their many moods with pencil on paper. Now subjects can tap on words like amused or relieved to record their emotions with stylus on handheld computer screen.There\u2019s a triple benefit: First, participants like using PDAs more than paper. Second, it\u2019s easy to tabulate results. And third, the time-stamped entries are more accurate, says Eshkol Rafaeli, a New York University postdoctoral fellow who coauthored the study "Diary Methods: Capturing Life as It Is Lived" (Annual Review of Psychology, 2003).Instead of spending 10 hours a day for months entering and rechecking data manually, researchers can quickly download the information onto their PCs. And they know for sure when a person answered a question and how long it took.The time stamp is crucial to Lisa Feldman Barrett, a Boston College psychology professor. The PDAs tell Barrett how long her subjects took to respond; if some adjectives were checked off quickly, that person may be more aware of his feelings. "Being precise about your emotions helps you to regulate your feelings and have strong social relationships, and it improves work efficiencies," she says.About five years ago, Barrett and her software engineer husband developed freeware called the Experienced Sampling Program (ESP, available at www2.bc.edu\/barretli\/esp\/index.html). ESP can randomize answers (it\u2019s boring for a study subject if 35 emotions, from "active" to "calm," look the same 12 times a day for a month) and beep the participant when it\u2019s time to answer. Future enhancements may depend on grant funding. Barrett says that could hinder how quickly her PDA application progresses; ideas for future projects include recording connections between a person\u2019s feelings and his heart rate, or even his facial expressions and voice.