I can think of a few reasons why you could get different results in addition to the strips being past their expiration date:
- especially as you have just eaten, there is a possibility you have some carbs on some of your fingers which would affect the readings
- our meters are not super accurate. Let's say the actual number was exactly in the middle: 10.1. The values you got varied about 13% from this. I have read that meters give results within 15%.
- within the tolerance from the last point is also the consideration that your BG may actually be rising or falling. For example, when I have just completed 30 minutes of intensive exercise, my BG often drops 2 units within 10 minutes if I don't topped it up with something sweet. Likewise, especially after a hypo, I expect my BG to rise sharply after some glucose tablets.