The Counterfeit Coins Riddle

There are 10 stacks of coins. Each stack contains 10 coins of the same value. However, one of the stacks is made entirely of counterfeit coins. You know that one counterfeit coin weighs one gram more than a genuine coin, and you know how much a genuine coin should weigh. You can weigh the coins on a pointer scale. What is the smallest number of weighings needed to identify the counterfeit stack? Explain.