The dynamic limitations of eye movement recorders can distort the measurement of fast eye movements such as saccades and nystagmic quick phases. In this paper, the effects of the bandwidth and noise of recording methods and the problems incurred by digital sampling are discussed theoretically with respect to the measurement of peak velocity and duration offast eye movements. As a practical example, a TV-based infrared corneal reflex system is examined and a method for calibrating it for peak velocity measurement is described.The measurement of eye movements (EMs) is becoming increasingly relevant in fields other than those concerned with the analysis of the oculomotor system itself. For example, correlations between unusual EMs and neurological pathologies have been made by Hamann (1979) and Zee, Optican, Cook, Robinson, and Engel (1976). There is also a large body of literature on the relationship between reading and EMs (e.g., Levy-Schoen & O' Regan, 1979). Furthermore, EM measurement is beginning to be usedin the developmental studyof the human infant (Aslin & Salapatek, 1975;Hainline, 1981). Each application of EM measurements has its own technological priorities. Some research questions require that the measuring system have great speed and resolution, whereas others require that intrusiveness upon the subject be minimized. In most current systems, there is a tradeoff among resolution, intrusiveness, and, of course, cost.The various instruments and their meritshave been discussed elsewhere (e.g., see Young & Sheena, 1975, for a comprehensive review). However, for efficientprogress, it is essential to be able to compare data from different instruments in different settings. To this end, McConkie (1981) stressed the need for investigators to report the quality of their data, such as sampling rate, drift, noise, accuracy, and short-and long-term repeatability. But such reporting necessitates an intimate understanding of one's EM recording instrument.The needfor calibrating an instrument so that the direction of the subject's eyeis precisely mapped onto stimulus space is self-evident, and there are various schemes for doing this (Bullinger & Kaufmann, 1977) Goldman-Rakic, 1981).It is less appreciated, though, that even an accurate mapping procedure does notcalibrate the instrument for all purposes. For example, during measurement of fast EMs such as saccades or nystagmic quick phases, the bandwidth and noise of the recording system can degrade the recording of dynamic responses. The most commonly used parameters for describing fast EMs are peak velocity (PV) and duration. In this paper, wediscuss the general effects of a system's bandwidth and noise on the measurement of these twoparameters of fast EMs. As an example, we present the results of a dynamic calibration of a TV-based, infrared, corneal-reflex system (Hainline, 1981) for the measurement of PV. Although this kind of instrument is certainly less than ideal for recording fast EMs, it has. the advantage of being nonintrusive to the subject, which makes...