The market high in 2007 was a textbook example of A/D line analysis. After the February drop (see Figure 2), the A/D line rebounded sharply, and by March 20 (line 1), it had already moved above the previous high, line a.
The A/D line was again leading prices higher, as the sharp rally continued into early June when the A/D line made its bull market high at point 2.
The A/D line developed support in June and July, line c, but when SPY made a new high on July 17, the A/D line failed to make a new high (point 3). This bearish divergence is illustrated by line b.
The A/D line dropped sharply into the August lows and moved well below its weighted moving average. (The wide gap between the A/D line and its WMA was indicative of an oversold market.)
By early September, the A/D line was again in an uptrend (higher highs and higher lows), and on October 11, 2007, SPY hit a high of $157.52, but the A/D line was much lower (point 4). The A/D line had just rallied back to its downtrend, line b, and the former support (now resistance) at line c.