understanding my meter readings

I have most recently come to the UK from America. the meters here read differently then I am used to. I was told that my BG should be between 6 and 9. A BG of 6 is actually a 60 and a low number. A 9 being about 80 which is normal. I am glad to have the challenge to keep my numbers in the range of 6 to 9 because it only means I will be healthier. My only problem is my BG has been dropping drastically in the last two weeks my lowest being 2.5. Do you know what that reading translates into American .
When I first received my meter I tested with both to compare them so I could understand the readings but I had not dropped that low. I have a Acu-check Aviva

Thank you