A more common representation of octave bands is on a horizontal logarithmic scale, so that each octave band has the same physical width-even though each successive band includes a frequency range that is double the previous one. The sound pressure level of each band is the sum total of all sound pressure levels in that band, not the average. The sound pressure levels for all bands in the spectrum can then be added up to calculate the overall sound pressure level, shown in the column to the right, in this case 84 decibels. Octave bands are obtained directly by measuring the sound with an octave band analyzer. This instrument groups sound pressure levels by frequency in the various octave bands.