The collection of data repeatedly from the same unit is very common in many biological experimental situations, for example liveweights of animals, composition of soil-core segments, counts of insects and pathogens in orchards, and the measurement of hormone levels and concentrations of pollutants in fresh and sea waters. This book explains both the proper design and the correct interpretation of such data acquisition. This is designed to serve as a practical handbook for biologists and gives up-to-date and relevant examples that should help biologists to plan their experiments in a more fruitful way.