CGMs and BGMs measure glucose in different places. CGMs read glucose in your interstitial fluid (the fluid around your cells), while BGMs measure glucose directly from your blood. Because glucose reaches the blood before it reaches the interstitial fluid, the numbers won’t always match, especially when your glucose is changing quickly (like after eating or exercising). This difference is normal and expected. Everyday factors like pressure on the biosensor and vitamin C can impact CGM readings, and things like unwashed hands or expired strips can affect readings from BGMs.