Glossary & Terminology

1. Physical Units & Coordinate Basics

1. 01
   SOG (Speed Over Ground): boat speed over ground in knots (kts). 1 knot = 1 nautical mile per hour (1 nm = 1,852 metres).
2. 02
   COG (Course Over Ground): movement direction derived from GPS fixes in degrees (0°–360°). It represents displacement direction, not bow heading.
3. 03
   TWD & TWS: True Wind Direction (the direction wind blows FROM, 0°–360°) and True Wind Speed in knots.
4. 04
   DDM Coordinates: Degree-Decimal-Minutes (e.g. 24°57.925'N, 118°42.310'E), the international maritime navigation standard.

2. Progress & Tactical Metrics (VMG, MMG, Loss)

1. 01
   VMG (Velocity Made Good): velocity projected onto a reference axis. Wind-axis VMG projects onto the true wind direction; Course VMG projects onto the direct line to the next mark; Bisector VMG projects onto the turn bisector.
2. 02
   MMG (Miles Made Good): net distance made good along a specified reference axis over a time window, distinct from total sailed track length.
3. 03
   Loss (Maneuver Loss in metres): expected progress based on steady straight-sailing baseline minus actual net progress along the turn bisector. Negative Loss is a gain against that baseline; positive Loss is a penalty.
4. 04
   Leg Time Gap: elapsed duration difference on that specific leg against the fastest boat, isolated from mark arrival timestamp differences accumulated earlier.

3. Boat Sides vs. Course Sides

Port and Starboard describe the boat's tack and which side receives the wind. Left, Middle, and Right in course-side analysis describe geographic positions across the sailing field looking upwind. They are independent concepts and must not be confused.