My diabetic grandfather's blood sugar level two hours after eating is 470 mg/dl. he says he feels okay. does he need medical attention?

Yes, but . . .: Post-prandial (after meal) blood sugar should not be greater than 200mg/dL, even if you/he feel(s) nothing. While not an emergency, it's best that he see his Family Doc as soon as possible to discuss nutrition & medication adjustment. Because he can always out eat any medication we prescribe, it's always best to start w/nutrition 1st. If sugars normally under control, then look 4 hidden infection

See a MD: He need to be seen by a MD. He will need following at least: 1) check device if working good 2) fasting blood sugar 3)Hb A1c level 4) all diabetic medications and dosages 5) compliance with treatment and diet