A good way to determine the general calibration of your particular meter is to compare the 30-day average that it stores to your HbA1c. Record the 30-day average in your meter on the day you have the blood draw.
Compare your 30-day average reading using a conversion chart of HbA1c percentage to blood sugar level.
Then, you know the AVERAGE error of your meter and your measurement technique and have a calibrated setup.
The thing to remember is that the meter's purpose is for you to adjust your inputs, your diet, your exercise, insulin (if you use it). Oral meds are not usually "adjusted" by daily readings, but by the HbA1c itself.
And, that the goal is a long-term goal, not a daily goal. It matters little if the measurement accuracy is +/- 20 percent. Because it's going to be high some times, and low some times. So, in the long-term, it averages out....
What I suggested to you about the 30-day average will tell you how many times it's high versus how many times it's low. This is useful for you to know. If you know that your meter is "biased" high, then you can use the readings by subtracting a little "fudge factor". If you know it's biased low, then add a little fudge factor....
Also, I know it should be under 160 after eating 2 hours, but what should it be at 4 hours????? Should it continue to go down?????
The thing to remember about this is that in diabetes, the rules become exceptions. Yes, in a healthy person, the reading will continue to go down. In fact, in a healthy person a couple hours after eating, the level won't be 160 either.
My guess is for you that you should have 120 4 hours after a meal if you have 160 at two hours. It's only a guess, mind you, but in general, your reading will go down. How rapidly is the problem of diabetes.....