Smudgy, it's frustrating. One day I do fine with eggs, the next not. Same with bread and rice. I was constantly getting high readings with rice so didn't eat it for ages. One night tried it again and got a 5.5 and then again a few nights later got a 7.5, so maybe it also depends on other things you have had through out the day. I wish there was a magical answer, but there doesn't seem to be!
I know what you mean about shaking the machine to make sure it's working ok! lol Especially this morning when I had a 3.2 fasting level. Took it again and got a 3.6, so it was low but that's strange. I'm rarely under 5.