Ever increasing network speeds and tighter loss budgets make qualifying multimode fiber links a formidable challenge. Part of the challenge can stem from test instruments. In some scenarios different test instruments can produce different measurement results on the same network due to variations in launch conditions between test sources. Encircled Flux (EF) standards, TIA-526-14-B and IEC 61280-4-1 Ed. 2.0, define a method of controlling multimode launch conditions for optical test sources. More consistent test source launch conditions equate to more accurate and repeatable measurements. This is the goal driving the migration to encircled flux standards.