Are you using the same brand electrodes/test sticks and from the same box/container.? Eating at the same hour, same protein sources ie animal origin or vegetable origin. Maybe you are eating close to your upper limit of prorein intake?. Sometimes I experience some differences , but all within the allowed limits of accuracy for home testing glucometers . I need to be be VERY VERY strict with macronutrient control to maintain good and stable BG readings.