The international radiotelephony urgency signal. When repeated x 3, indicates uncertainty or alert, followed by nature of urgency.
Related Terms 
DIRECTION LIGHT
A light illuminating a sector of very narrow angle and intended to mark a direction to be followed. A direction light bounded by other sectors of different characteristics which define its margins with small angles of uncertainty is called a SINGLE STATION RANGE LIGHT.

UNCERTAINTY
Refers to the difference between measurement by a field instrument and the 'true' or 'actual' quantity being measured.

INCERTFA
A SAR uncertainty phase requiring monitoring and intelligence gathering for more task information.

INTELLIGENT MACHINE
Any machine that can accomplish its specific task in the presence of uncertainty and variability in its environment.

CB
Block coefficient  a measure of the fullness of the form of the ship and is the ratio of the volume of displacement to a given waterline, and the volume of the circumscribing solid of constant rectangular crosssection having the same length, breadth and draught as the ship. CB= (L x B x T) The LPP is normally used in calculating the value of CB which varies with the type of ship. Fast ships Ordinary ships Slow ships 0.500.65 (fine form) 0.650.75 (moderate form) 0.750.85 (full form)

CELSIUS TEMPERATURE SCALE
Temperature scale of 0o (freezing water) to 100o (boiling water). Celsius = (Fahrenheit  32) x 5/9.

FAHRENHEIT
Imperial scale of temperature. Fahrenheit = ((9 x Celsius) 5) + 32

LANE METRE
A 1.0 metre in length x 2.0 metre in width area of deck (linear metre) used in assessing capacity of Ro/Ro ships.

MIDSHIP SECTION AREA COEFFICIENT
(CM): The ratio of the immersed area of the midship section to the area of the circumscribing rectangle having a breadth equal to the breadth of the ship and a depth equal to the draught. CM = AM (B x T), CM values range from about 0.85 for fast ships to 0.99 for slow ships.

ROLLING TEST
An approximate method of calculating a vessels GM. GM in mtrs = ((F x breadth)x(F x breadth)) Time in secs F = 0.78  0.98 dependant on hull shape.
