As longtime readers of this column know, I strongly believe that when you launch a new business, it's important to track monthly sales and gross margins by hand for the first year or two. I tell people, "Don't use a computer. Write down the numbers. Break them out by product category or service type and by customer. And do the math yourself, using nothing more sophisticated than a calculator." To be successful in any business, you need to develop a feel for the numbers. You need to get a sense of the relationships between them, see the connections, figure out which ones are critical and have to be monitored. Why? Because numbers run businesses. They tell you how you can make the most money ...