Measuring is a procedure to obtain useful information on objects and processes. A good example is provided by the so-called speech chain. The speech chain concept is well known among speech therapists and phoneticians. This chapter suggests that there is a clear dichotomy in measuring: subjective (human) vs. objective (instrumental). The effects of these commands are the initiation of airflow, settings of the laryngeal system resulting in either phonation or non-phonation, and the movement and positioning of the articulators. Thus, with different parameter settings, one might obtain different voice decisions and consequently different measures of voice irregularity, called jitter. This means that all measurements, be they subjective or instrumental, involve the following requirements: validity, sensitivity, reliability, and agreement. Conventionally, there are four types or levels of measurement scales on which objects can be measured: nominal, ordinal, interval and ratio scales. The chapter also presents an overview on the key concepts discussed in this book.