What is the primary function of the Admiralty Chart Datum (ACD)?

The primary function of the Admiralty Chart Datum (ACD) is to measure water depths on nautical charts. The ACD provides a consistent reference point for underwater measurements, ensuring that depth data is related to a standardized level. This is critical for safe navigation, as it allows mariners to understand the vertical clearance of their vessels when plotting courses through navigable waters.

By using the datum, hydrographers can accurately depict the depths of a water body, taking into account various factors such as tides and seasonal changes. This reliability in depth representation helps prevent grounding and other navigational hazards, making it a fundamental aspect of hydrographic surveying and nautical charting. The ACD is based on a specific vertical reference, typically low water level, allowing for standardized readings across different regions.