Cloud cover Cloud cover Cloud cover (also known as cloudiness, cloudage, or cloud amount) refers to the fraction of the sky obscured by clouds when observed from a particular location. Okta is the usual unit of measurement of the cloud cover. The cloud cover is correlated to the sunshine duration as the least cloudy locales are the sunniest ones while the cloudiest areas are the least sunny places. The global cloud cover averages around 0.68 when analyzing clouds with optical depth larger than 0.1. This value is lower (0.56) when considering clouds with an optical depth larger than 2, and higher when
Coherence (units of measurement) Units (1960) was designed around the principle of coherence. In SI, which is a coherent system, the unit of power is the watt, which is defined as one joule per second. In the US customary system of measurement, which is non-coherent, the unit of power is the horsepower, which is defined as 550 foot-pounds per second (the pound in this context being the pound-force); similarly the gallon is not equal to a cubic yard (nor is it the cube of any length unit of the system). The earliest units of measure devised by humanity bore no relationship to each other.