(stockchart.com)
Support and resistance are like mirror images and have many common characteristics.
Highs and Lows
Support can be established with the previous reaction lows. Resistance can be established by using the previous reaction highs.
The above chart for Halliburton (HAL) shows a large trading range between Dec-99 and Mar-00. Support was established with the October low around 33. In December, the stock returned to support in the mid-thirties and formed a low around 34. Finally, in February the stock again returned to the support scene and formed a low around 33 1/2.
After each bounce off support, the stock traded all the way up to resistance. Resistance was first established by the September support break at 42.5. After a support level is broken, it can turn into a resistance level. From the October lows, the stock advanced to the new support-turned-resistance level around 42.5. When the stock failed to advance past 42.5, the resistance level was confirmed. The stock subsequently traded up to 42.5 two more times after that and failed to surpass resistance both times.
Support Equals Resistance
Another principle of technical analysis stipulates that support can turn into resistance and visa versa. Once the price breaks below a support level, the broken support level can turn into resistance. The break of support signals that the forces of supply have overcome the forces of demand. Therefore, if the price returns to this level, there is likely to be an increase in supply, and hence resistance.
The other turn of the coin is resistance turning into support. As the price advances above resistance, it signals changes in supply and demand. The breakout above resistance proves that the forces of demand have overwhelmed the forces of supply. If the price returns to this level, there is likely to be an increase in demand and support will be found.
In this example of the NASDAQ 100 Index ($NDX), the stock broke resistance at 935 in May-97 and traded just above this resistance level for over a month. The ability to remain above resistance established 935 as a new support level. The stock subsequently rose to 1150, but then fell back to test support at 935. After the second test of support at 935, this level is well established.
From the PeopleSoft (PSFT) example, we can see that support can turn into resistance and then back into support. PeopleSoft found support at 18 from Oct-98 to Jan-99 (green oval), but broke below support in Mar-99 as the bears overpowered the bulls. When the stock rebounded (red oval), there was still overhead supply at 18 and resistance was met from Jun-99 to Oct-99.
Where does this overhead supply come from? Demand was obviously increasing around 18 from Oct-98 to Mar-99 (green oval). Therefore, there were a lot of buyers in the stock around 18. When the price declined past 18 and to around 14, many of these buyers were probably still holding the stock. This left a supply overhang (commonly known as resistance) around 18. When the stock rebounded to 18, many of the green-oval-buyers (who bought around 18) probably took the opportunity to sell. When this supply was exhausted, the demand was able to overpower supply and advance above resistance at 18.
