Varying results with contourXT meter

[Gobiker56]

I got a new contour xt meter a few days ago. The results on my meter are quite different to the results of the nurses meter in the local surgery. I measured about 2 hours before I went and got 107 mg/dl. the surgery got 140. I tested again at after lunch 14.25 and got 52 mg/dl, so I did another immediately and got 73 mg/dl ,an hour later I got 99 mg/dl. Being a newbie I am not sure which readings to believe. Could I be doing something wrong?.or can your blood sugar vary so much in such a short time or is the machine faulty?. I am on Velmetia 50mg/1000mg twice a day and Gliclazida (mylan) 30mg 2 with breakfast and 1 with lunch..