double-dotted 8th notes

I was just looking at MIDI/Simple.pm's %Length hash:

  'wn' =>  4,     'dwn' => 6,    'ddwn' => 7,       'twn' => (8/3),
  'hn' =>  2,     'dhn' => 3,    'ddhn' => 3.5,     'thn' => (4/3),
  'qn' =>  1,     'dqn' => 1.5,  'ddqn' => 1.75,    'tqn' => (2/3),
  'en' => .5,     'den' => .75,  'dden' => .75,     'ten' => (1/3),
  'sn' => .25,    'dsn' => .375, 'ddsn' => .4375,   'tsn' => (1/6),

and I've looked at this a million times before, but today I just happened 
to notice: that says an 8th note is half a quarter note, and a dotted-8th 
is .75 of a quarter note, AS IS a double-dotted 8th note?!  That can't be 
right, can it?
Shouldn't a double-dotted 8th note be... um... 7/8ths of a quarter 
note?  7/16ths?  Aaaaaaaa Rickeeeee music theory hurts my head waaaaaaa...
--
Sean M. Burke    http://search.cpan.org/~sburke/