Before you can calculate water vapor, you must first look up the calibration constants for your instrument here. If you cannot find your water instrument in the file of calibration constants, it has not yet been calibrated. There are 5 values: A, B, C, β, and τ. Of these five values, only A is different for every instrument, and is not given a default value in the table below. The other four parameters are given default values. In some cases, the B value for your instrument may be slightly different from the one shown as a default value, and you can change it as required. Unless you have discussed using different values for C, β, and τ with the Science Team, do not change these values.
The longitude and latitude given as default values applies to the "home site" for these instruments in Philadelphia, Pennsylvania, USA. Longitudes in the western hemisphere have negative values and northern hemisphere latitudes are positive. When you change the coordinates for your site, remember to express angles as decimal degrees, not degrees, minutes, and seconds, or degrees and decimal minutes. If you are using a GPS receiver to obtain longitude and latitude, you may need to access your receiver's setup menu to change how degrees are displayed.
A table entry is reserved for barometric pressure. At some time in the future, the PW calculations may be revised in a way that will use this value. For now, you can leave the default value (standard sea level pressure) unchanged.