Why is Ref 0 calculation different with split markers?

The calculation of Ref 0 with split markers is significant because it is designed to account for more complex performance scenarios that involve two engines. When calculating performance metrics, particularly during takeoff, it's important to consider how each engine contributes to acceleration and overall aircraft performance. With split markers, the Ref 0 calculation adjusts for the acceleration characteristics of the aircraft when both engines are producing thrust, ensuring more accurate performance data for safe and efficient operations.

This approach reflects operational realities where both engines are engaged and helps pilots and flight planners to better understand how the aircraft will perform under different conditions. It emphasizes the importance of dual-engine performance parameters over those that would only consider a single-engine scenario, which could potentially lead to conservative estimates and an underestimation of aircraft capability in certain situations.

The other options do not apply to this calculation context, as they focus on either other performance assumptions or conditions that are not directly related to how the engines operate together during the calculation of Ref 0.