Why blood sugar testing kit shows 2 different result if i take the second one right after the first one?

Life is not exact: Lab tests give a number (display a result) that is a close estimate of the real value. That means a drop of blood has a blood sugar level in it, but doing 2 tests on that one drop of blood will display 2, usually different, numbers - each of which is an estimate of the blood sugar level in that one drop of blood. That's basically how lab tests work.