δ vs easting (left/top) and vs line length (right/bottom). The 1″ threshold line is shown dashed in ochre. δ grows with L² and with distance from CM. For short cadastral lines (<5 km) in Zone 50, δ is typically <0.5″. Formula: δ ≈ |E−500000|·L²/(6·R²·k₀) arcseconds.