The AD Line and AD Volume Line are aggregate measures of participation. The AD Line favors small and mid-caps because an advance equals +1 and a decline equals -1, regardless of market cap. This means an advance in Apple ($556 billion market cap) counts the same as an advance in Digital River ($475 million market cap). The AD Line is a summation of net advances (advances less declines) for each day. An uptrend in the AD Line indicates broad participation in an advance.