Dead Reckoning position: After a fix is obtained, the next position of the vessel which is found by applying course steered, leeway and engine speed ONLY is called Dead Reckoning position. This is denoted by the symbol 'X'.
Estimated Position: If the DR position (obtained above) is adjusted for prevailing set and expected drift then the position is said to be Estimated Position. This is denoted by the triangle symbol.
Observed position or FIX: The actual position of the ship is called as the Observed Position or Fix. This is denoted by a Circle. The OP or Fix is the most accurate position of the ship.Also read this - What all factors affect the squat of vessel?
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