58 INSTRUCTIONS TO MARINE METEOROLOGICAL OBSERVERS 



Symbols pp — Barometer change 



[Amount of rise or fall of the barometer in the last three hours] 



Sliould the value of the variation be 20,0 millibars or more, "pp" 

 should be reported as 99, and the actual amount of the tendency, 

 without regard to sign, should be given at the end of the report in 

 plain language, e. g., "Tendency 23.8 millibars." 



Form of 'predoininating cloud (C). — When two or more layers of 

 clouds are visible, the predominating clouds are those which cover 

 the largest proportion of the sky. Their form is to be determined 

 by referring to the descriptions and photographs in Part V. The 

 table below, which is to be used Avhen this information is transmitted 

 by radio, gives the code numbers corresponding to the various forms 

 of clouds. 



Symbol C — Form of predominating cloud 



