The CGM doesn't test blood glucose in the same way as the meters - it tests some other fluid just under the skin - sorry not an expert on this! I think the meter tests show what the actual BG is at the time of the test whereas the CGM shows what it was a short while ago. From what I've read, people with CGMs do have to test their blood as well as using the CGM to confirm that the CGM is reading accurately. As I say, I'm no expert in this, so hopefully someone who is will come along and answer the question.
Smidge