Time lag between the source text input and the interpreter’s target text is known as ear-voice span or décalage. Recently, time lag has also been measured in written translation based on eye-tracking and key-logging (hence called eye-key span). Time lag provides insight into the temporal characteristics of simultaneity in interpreting, speed of translation and also into the cognitive load and cognitive processing involved in the translation/interpreting process. Ear-voice span/eye-key span (EVS/EKS) thus have the potential to become very valuable measures in translation/interpreting process-oriented research, but more needs to be known about their properties and the information this metric yields. Several exploratory analyses were carried out to compare methods used in previous research and to address the questions of EVS/EKS variability among participants, stability of EVS/EKS over the course of an individual’s performance, and variation in EVS/EKS at different points of measurement and across different tasks performed by the same person. The results indicate that EVS/EKS is indeed a sensitive measure useful for process-oriented research. Finally, some methodological challenges and procedures for both interpreting and translation are discussed.