anchor.diff:      , mean      = 0.0       :: float()
       , m2        = 0.0       :: float()
       , delta     = 0.0       :: float()
  +    }).
  +    
  +    
  +-record(stream_sample,
  +    { size      = 1         :: pos_integer()
  +    , count     = 0         :: type:natural()
  +    , data      = {}        :: tuple()
       }).
   
   
  
positive.code: stddev_values( #stream_stddev{ mean = Mean } = X )  ->
      { Mean, math:sqrt( stddev_variance(X) ) }.
  
  
  %%%%% ------------------------------------------------------- %%%%%
  
negative.code: 
  -module(stream).
  
  -export([stddev_new/0, stddev_push/2, stddev_variance/1, stddev_values/1, stddev_samples/1]).
  -export([sample_new/1, sample_update/2, sample_values/1]).
  
  
  %%%%% ------------------------------------------------------- %%%%%
  