Encoding the Pressure
On the recording sheet, enter the sea level pressure in hectopascals (hPa) using tens, units, and tenths (without the decimal). For instance, to record 1035.1 hPa, you would enter 351. To record 1015.75 hPa, you would enter 157.
Altimeter setting should be reported in inches of Mercury (inches Hg) using tens, units, tenths, and hundredths (without the decimal). To record 29.96 inches Hg, enter 2996.
Station pressure should be reported to the nearest 0.005 inch Hg on each hourly observation. For example, 29.995 in Hg or 30.125 in Hg.
For any of the pressure measurements, enter "M" if the value is missing. For altimeter setting and station pressure, prefix the observation with an "E" if the data are estimated.