Advance/decline line

Example

Say an exchange’s A/D line stands at 12,000. For five sessions the index edges higher, yet each day 1,600 stocks fall and 1,400 rise, so the line drops 200 a day, to 11,000. The 12,000 means nothing on its own, since it depends on the start date; what matters is the line falling while the index rises, a sign that fewer stocks are joining the move.

Hypothetical numbers, for illustration only.