What should a pilot focus on during performance cross-checking?

During performance cross-checking, the pilot should focus on confirming that all flight instruments agree. This is essential because cross-checking involves comparing readings from various instruments to ensure consistency and accuracy. Discrepancies between instruments can indicate potential errors or malfunctions, which is crucial for safe flying. When a pilot verifies that all instruments provide similar information, it promotes situational awareness and helps in making informed decisions regarding aircraft performance and navigation.

The other options, while relevant to aviation, do not capture the essence of performance cross-checking. Monitoring altimeter readings alone would not provide a complete picture. Ensuring all flight instruments are calibrated is important, but it is a part of pre-flight checks rather than ongoing cross-checking during flight. Counting the number of passengers onboard, while a part of weight and balance considerations, does not relate to performance monitoring of the aircraft in flight. Thus, focusing on the agreement between instruments is fundamental during performance cross-checking to maintain safe operations.