Abstract: A wearable blood glucose monitoring device, apparatus, and method of measuring a blood glucose level are provided. The method includes an oscillator assembly that transmits microwaves at an oscillator frequency based on an input impedance. The input impedance is associated with the permittivity of blood in a user's blood vessel. The method also includes a frequency detection circuit that detects a first oscillator frequency at a first time and a second oscillator frequency at a second time. The method further includes a main control board that receives an indication of a user's condition, compares the first oscillator frequency with the second oscillator frequency to determine a frequency drift, calibrates the frequency drift based on the received indication of the condition of the user, and determines a blood glucose level of the user based on the calibrated frequency drift. A corresponding wearable blood glucose monitoring device and apparatus are also provided.