Bad pressure absolute pressure values

The BF operator noted that the sonde pressure was reading about 20 hPa low
relative to ambient.  Based on interpolation from the previous and subsequent
soundings, the surface pressure was probably something like 978 hPa.  The
sonde pressure sensor was reading 955.8.  It is possible that the operator
used the wrong calibration tape, but it is more likely that their was
a problem with the pressure sensor (based on the reasonable values of
surface temperature and rh).

• Relative Humidity (hybrid-b grid)(rh)
• Wind status(wstat)
• Wind Direction(deg)
• Easterly Wind Component(u_wind)
• lon(lon)
• -180.0 - +180.0(alt)
• base time in epoch(base_time)
• Retrieved pressure profile(pres)
• Wind Speed(wspd)
• Time offset from base_time(time_offset)
• Ascent rate(asc)
• North Latitude(lat)
• Dry Bulb Temperature(tdry)
• Dewpoint Temperature(dp)
• V wind component(v_wind)