code: function(str, vtg) {
  
        if (vtg.length !== 10 && vtg.length !== 11) {
          throw new Error('Invalid VTG length: ' + str);
        }
  
        /*
         ------------------------------------------------------------------------------
         1  2  3  4  5  6  7  8 9   10
         |  |  |  |  |  |  |  | |   |
         $--VTG,x.x,T,x.x,M,x.x,N,x.x,K,m,*hh<CR><LF>
         ------------------------------------------------------------------------------
         
         1    = Track made good (degrees true)
         2    = Fixed text 'T' indicates that track made good is relative to true north
         3    = optional: Track made good (degrees magnetic)
         4    = optional: M: track made good is relative to magnetic north
         5    = Speed over ground in knots
         6    = Fixed text 'N' indicates that speed over ground in in knots
         7    = Speed over ground in kilometers/hour
         8    = Fixed text 'K' indicates that speed over ground is in kilometers/hour
         (9)   = FAA mode indicator (NMEA 2.3 and later)
         9/10 = Checksum
         */
  
        if (vtg[2] === '' && vtg[8] === '' && vtg[6] === '') {
  
          return {
            'track': null,
            'trackMagetic': null,
            'speed': null,
            'faa': null
          };
        }
  
        if (vtg[2] !== 'T') {
          throw new Error('Invalid VTG track mode: ' + str);
        }
  
        if (vtg[8] !== 'K' || vtg[6] !== 'N') {
          throw new Error('Invalid VTG speed tag: ' + str);
        }
  
        return {
          'track': parseNumber(vtg[1]), // heading
          'trackMagnetic': vtg[3] === '' ? null : parseNumber(vtg[3]), // heading uncorrected to magnetic north
          'speed': parseKnots(vtg[5]),
          'faa': vtg.length === 11 ? parseFAA(vtg[9]) : null
        };
      }
docs: Track info