def delta(other_audit)
    
      return self.change_log if other_audit.nil?
    
      {}.tap do |d|
        
        # first for keys present only in this audit
        (self.change_log.keys - other_audit.change_log.keys).each do |k|
          d[k] = [nil, self.change_log[k]]
        end
    
        # .. then for keys present only in other audit
        (other_audit.change_log.keys - self.change_log.keys).each do |k|
          d[k] = [other_audit.change_log[k], nil]
        end
    
        # .. finally for keys present in both, but with different values
        self.change_log.keys.each do |k|
          if self.change_log[k] != other_audit.change_log[k]
            d[k] = [other_audit.change_log[k], self.change_log[k]]
          end
        end
    
      end

    end
def delta(other_audit)
    
      return self.change_log if other_audit.nil?
    
      {}.tap do |d|
        
        # first for keys present only in this audit
        (self.change_log.keys - other_audit.change_log.keys).each do |k|
          d[k] = [nil, self.change_log[k]]
        end
    
        # .. then for keys present only in other audit
        (other_audit.change_log.keys - self.change_log.keys).each do |k|
          d[k] = [other_audit.change_log[k], nil]
        end
    
        # .. finally for keys present in both, but with different values
        self.change_log.keys.each do |k|
          if self.change_log[k] != other_audit.change_log[k]
            d[k] = [other_audit.change_log[k], self.change_log[k]]
          end
        end
    
      end

    end
Computes the differences of the change logs between two audits.

 Returns a hash containing arrays of the form
   {
     :key_1 => [<value_in_other_audit>, <value_in_this_audit>],
     :key_2 => [<value_in_other_audit>, <value_in_this_audit>],
   }