# Overcoming Individual Discrepancies, a Learning Model for Non-Invasive Blood Glucose Measurement
## 2 Related Works
### Mini-Invasive  
_FreeStyleTM Libre_: This is a wearable continuous glucose monitoring device from Abbott, and consists of a coin-sized disposable circular sensor that is attached to the upper arm by a miniature needle of \(5.0\) mm long and \(0.4\) mm wide and a small adhesive tape. The user can obtain his/her blood glucose level through a handheld device. It should be noted that this product measures the glucose concentration of the interstitial fluid, which exists a time lag compared to blood glucose level, which means that a finger trick test using a blood glucose meter is required during times of rapidly changing glucose levels when interstitial fluid glucose levels may not accurately reflect blood glucose levels, or if hypoglycemia or impending hypoglycemia is reported but the symptoms do not match the system readings [6]. In addition, _FreeStyle\({}^{\text{TM}}\)_ _Libre_ needs to be replaced every 14 days, to avoid wound infection.  
_Symphony\({}^{\text{TM}}\)_: It was developed by Echo Therapeutics, Inc., as a mini-invasive continuous glucose monitoring device. A special skin preparation device is used to permeate the skin before placing the sensor. The device abrades the skin, removing about 0.015 mm of the outer layer of skin using adaptive micro-abrasion technology. This process takes 10-20 s, and removal of the outer layer of skin for allowing the measuring of a number of physiological properties, including interstitial glucose levels. All the measured values are transmitted wirelessly to a remote monitor that is equipped with alarm alerts if the glucose level is outside the normal range. Like _FreeStyle\({}^{\text{TM}}\)_ _Libre_, since _Symphony\({}^{\text{TM}}\)_ _measures the interstitial glucose levels, it also does not accurately reflect blood glucose levels.  
G5/G6\({}^{\text{TM}}\)_: Dexcom _G5/G6\({}^{\text{TM}}\)_ _is a patch device, and composed of three parts: A sensor that measures glucose in the fluid under the skin, a processor that is embedded on the sensor and transmits the data to the receiver every five minutes, and a receiver that displays the blood glucose level to the user [20]. The measurement principle of this device is similar to _FreeStyle\({}^{\text{TM}}\)_ _and_ _Symphony\({}^{\text{TM}}\)_ _, and is indicated by the FDA for use as both a standalone CGM and for integration into automated insulin dosing (AID) systems [21]._  
_GlucoWatch\({}^{\text{TM}}\)_: It is a watch-type glucose meter that contacts the human skin through an electrode, which generates a micro current to the skin. The charged ions and glucose in the subcutaneous interstitial fluid can migrate to the skin surface under the action of the electric field, and the glucose concentration is measured by glucose oxidase. This device has high requirements on the physiological condition of human body. Factors, e.g., skin sweating, environmental temperature, electrostatic interference, etc. will affect the measurement results. Due to its low accuracy, _GlucoWatch\({}^{\text{TM}}\)_ _has been revoked by the FDA and is required to recall products that have already been sold._