  Research on mobile phone use often starts with a question of "How much time
users spend on using their phones?". The question involves an equal-length
measure that captures the duration of mobile phone use but does not tackle the
other temporal characteristics of user behavior, such as frequency, timing, and
sequence. In the study, we proposed a variable-length measure called "session"
to uncover the unmeasured temporal characteristics. We use an open source data
to demonstrate how to quantify sessions, aggregate the sessions to higher units
of analysis within and across users, evaluate the results, and apply the
measure for theoretical or practical purposes.
