Does a person who doesn't have diabetes always have a blood sugar reading that stays
Below 120? Or can it bounce around up to 200 on the tester according to what you
Ate?

Normal is 80 to l20 and should stay in that range if you are controlling your diabetes with diet. If it is higher, then you are not controlling your diet well enough and should be more carefule. Are you on meds as well ?

If you are Not diagnosed with diabetes that your numbers will stay down below 120.

If it jumps to 200 There is something wrong and you need to have more tests (A1c tests can tell a good bit of info)of tests more often.

I you have the opportunity to test and are wondering:

You can test: fasting, 1 hr after breakfast, 2 hrs after, lunch, 1 hr after, 2 hrs after, dinner, 1 hr after, 2 hrs after and bedtime over about 3 days.

That will give a good clue.