When a stock splits, many charts show it similarly to a dividend payout and therefore do not show a dramatic dip in price. Taking the same example as above, a company with 100 shares of stock priced at $50 per share. The company splits its stock 2-for-1. There are now 200 shares of stock and each shareholder holds twice as many shares.
The price of each share is adjusted to $25. As a result, when looking at a historical chart, one might expect to see the stock dropping from $50 to $25. To avoid these discontinuities, many charts use what is known as an adjusted share price; that is, they divide all closing prices before the split by the split ratio. Thus, when looking at the charts it will seem as if the price was always $25. Both the Yahoo! historical price charts[2] and the Google historical price charts[3] show the adjusted close prices.