One of the key measurements of market sentiment is support and resistance. If resistance breaks, there are more bulls in the market at that time than bears. If it bounces, we know the bears have overpowered the bulls. Likewise, if a support level holds, we know that any drops in price were most likely caused by routine profit-taking. If it breaks, on the other hand, we know we have short sellers entering the market along with longs starting to close their positions.