With a device known as a Continuous Blood Glucose Monitor, a person with diabetes has greater insights on what their blood glucose levels are doing - how they rise and fall in reaction to those factors. We can also see how rapidly it changes, and take appropriate action (if necessary).
Below are two images captured from my iPhone that were transmitted by my Continuous Blood Glucose Monitor. One shows what somewhat desirable, though not perfect, blood glucose levels look like. The other shows what stress can do.