Ireland's Ancient Navigation System - Apparently.
The ancient Irish had a sophisticated navigation system that allowed them to accurately predict tidal patterns, as evidenced by the surviving manuscripts of the "Tonn Pádraig" (St. Patrick's Tides) from the 10th century. This manuscript contains tables that accurately predict tidal patterns for the Irish coast, often within a 10-minute margin of error. The system's accuracy is still debated among historians, but its existence and effectiveness are verifiable through archaeological and literary records.