The mechanisms between different BP monitors are slightly different. For home monitoring BP devices, usually after 2-3 years the accuracy will decrease and will need to be calibrated by the manufacturer.
Meanwhile, there are a lot of factors that could affect the blood pressure reading such as hydration, mood, position, stress level, environment, movement, cuff, etc. Even if you check your blood pressure with the same device, it could give you a slightly different reading. Therefore, it’s hard to compare between two devices. The most important thing for measuring BP at home is consistency, which means you need to use the same device to see the overall trend. If you still have concerns or questions about the readings, you can contact your care team or take both devices to the clinic and your care team can compare them side by side and also with a mercury sphygmomanometer, which is the golden standard measurement for BP.