The collection of a regular series of data points during a recording to enable the temporal variations of the measured values to be studied. This can be in a personal noise dosimeter, a heat stress monitor, a real time dust or particulate monitor or a weather monitoring system. All of these examples show the benefit of knowing when certain measured values occurred in order to apply corrective measures properly. Data logging can be done as rapidly as every second for fast changing acoustic signals or as slow as every hour for more slowly varying weather parameters such as atmospheric pressure.