The isobaric chart is a plot of meteorological data on a constant pressure surface.  The numerical value is given in millibars (mb), which is equivalent to the hectopascal (hPa).  It is the most common of the upper air charts on which rawinsonde data are plotted.  On the chart, you will find temperature (<sup>o</sup>C) on the upper left, dew point depression (<sup>o</sup>C) on the lower left, geopotential height (in meters) on the upper right, and a plot of the wind data (dddff format, where ddd is the wind direction, in 5 degree increments, and ff is the wind speed in knots) on the lower right.  In addition, the wind is plotted in the standard meteorological convention.