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One recent change being debated in the aviation community is to implement techniques, similar to free-flight which would allow pilots rather than air traffic controllers to retain more control of their flight paths, speeds, and separate themselves from other flights. By implementing ‘self-separation’, one of the positions most significantly affected is that of the air traffic controller due to changes in their job tasking in a ‘free flight’ environment. As the safe capacity of the National Airspace System is limited by the controller workload, it is essential to measure the workload changes accurately and in a way that can be compared between experiments. This paper outlines a method to compare three indices used to measure controller workload. These measures include the Instantaneous Self Assessment method (ISA), the NASA Task Load Index (NASA-TLX) and the Subjective Workload Assessment Technique (SWAT). Workload measures from all three workload indices are measured and then compared by using the coefficient of variance. The workload scores are compared to assess similarities and discuss how these results can be used to create a common standard of comparison to other workload research using these metrics.