<P> National Weather Service and TV / radio broadcast public forecasts, however, are given almost exclusively in customary units: degrees Fahrenheit for temperature and dewpoint, fractions of an inch of rain or ice and whole inches of snow (less than an inch often indicated by fractions or informal terms like "dusting" when very low), inches of mercury; and for wind speeds, miles per hour, except in marine forecasts, in which knots are used and wave heights are measured in feet . Actual sleet and snowfall and their depths on the ground are measured in tenths of an inch, with actual rainfall in hundredths, and ice accretion in either fractions or decimals . Barometer readings for hurricanes are usually given in millibars (mb), which are equal to hectopascals (hPa), or ten times the kilopascals (kPa) used in neighboring Canada; the use of inches of mercury in such applications is rapidly declining . </P> <P> In early 2007, NASA announced that it would use metric units for all operations on the lunar surface upon its return to the Moon, then projected for 2020 . However, NASA's lunar return program was canceled in 2010 . </P> <P> The medical field uses predominantly metric units . When interacting with patients certain data, such as their height and weight, is presented in customary units . </P> <P> Both prescription and non-prescription dosages of pills are always measured in the SI system with the most common unit being the milligram . Smaller dosages use micrograms . Because the SI prefix μ (mu) is not well known among many Americans and it isn't available on most keyboards the medical industry uses the abbreviation mcg to denote micrograms . </P>

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