Caterpillar (CAT -1.50%) just delivered one of the best earnings reports in the industrial sector this earnings season. As the chart below demonstrates, its stock price continues to rise. However, the question now is what will make the stock a buy for investors. Here's what you need to know. Three things to make Caterpillar a buy There are three key answers to this question, and I will flesh them out below: A lower stock price because Caterpillar's valuation is starting to look stretched. An improvement in ...