The EOG value varies from 50 to 3500 V with a frequency range of about dc-100 Hz. Its behavior is practically linear for gaze angles of . It should be pointed out here that the variables measured in the human body (any biopotential) are rarely deterministic. Its magnitude varies with time, even when all possible variables are controlled. Most of these biopotentials vary widely among normal patients, even under similar measurement conditions. This means that the variability of the electrooculogram reading depends on many factors that are difficult to determine: perturbations caused by other biopotentials such as EEG (electroencephalogram), EMG (electromiogram), in turn brought about by the acquisition system, plus those due to the positioning of the electrodes, skin-electrode contacts, lighting conditions, head movements, blinking, etc. In [14] various studies were made of the accuracy and precision of the EOG in tracking the eye gaze. To eliminate or minimize these defects, therefore, a considerable effort had to be made in the signal acquisition stage to make sure it is captured with the minimum possible perturbations and then during the study and processing thereof to obtain the best possible results.