# print method on pvol returns correct test

    Code
      cat(print(pvol))
    Output
                     Polar volume (class pvol)
      
           # scans:  3 
             radar:  seang 
            source:  WMO:02606,RAD:SE50,PLC:Angelholm,NOD:seang,ORG:82,CTY:643,CMT:Swedish radar 
      nominal time:  2015-10-18 18:00:00