What is a required piece of equipment for day VFR flight?

For day VFR (Visual Flight Rules) flight, certain equipment is mandated by regulations to ensure safe operation. The oil pressure gauge is essential because it provides critical information regarding the engine's oil pressure, which is crucial for maintaining engine health. A functioning oil pressure gauge helps pilots monitor whether the engine is operating within safe limits.

While other equipment like an altitude indicator is important for situational awareness and navigation, it is not explicitly required for day VFR flight under the regulations. The flight director and ground speed indicator, while useful, are also not mandatory for day VFR operations. This makes the oil pressure gauge a fundamental requirement as it directly relates to the engine's performance and safety.