How did people with DM control their glucose before meters were invented?

Meters that measured glucose by means of an instrument that measures refraction on an optical prism are really quite old. It is the new convenient digital ones that make frequent testing convenient. The main drug therapies for diabetes, metformin and glucophage are also fairly old as drugs go. Drugs like Beyetta are of a recent type. It has been know for a very long time that diet is the most important aspect of glucose control and remains so. It has been known for a long time that being overweight or obese is a major contributing factor and can be reversed by diet. More recently the role of insulin resistance of the body, especially the muscles has been proven to be as important as the supply of insulin. That is why exercise has been recently seen as more important.