Continuous Glucose Sensors are used to measure the blood sugars on a continuous basis. Blood sugar readings are obtained every 5 minutes. The readings are based on the sugar concentration in the interstitial fluid (the fluid that bathes our cells) and are made accurate by the process of calibrating (doing finger stick blood glucose and entering this number into the sensor system). These calibrations need to be done at least every 12 hours and can vary depending on the system you choose.