Farmer

A farmer has bought some camels and is taking them home. As he rides along, he counts them...

A farmer has bought some camels and is taking them home. As he rides along, he counts them: 29. He was sure he had bought 30, so he jumps off his camel and counts them again. To his delight, there are 30. Half an hour later, he counts his camels and once more, there are just 29. Confused, he climbs off his camel and counts again. Once more, there are 30. Can you explain?