@gulfcoast
Which symbol you mean? These ones ?

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The first one (Rain) is the quantity of rain received during 3 hours.
The second one (Rain accumulation) is the total quantity of rain received during the next 12h, 24h, 3 days... according to the scale at bottom of your screen.
The quantity of rain is expressed in mm (or in inch depending of your settings).

Or this one ?

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This is the Air Humidity, i.e. the amount of water vapor in air, expressed in % of the maximum amount the air can hold