Hi there! I've had the 640G since October. I've watched a video of how to insert the sensors/transmitter to get the most out of them... it involves making sure they are situated with the sensor pointing to the north or south. So up/down. And when the inserter is placed on the body, not pressing at all - just have it held lightly in place. Lots of problems are caused by the sensor or transmitter being able to move (being up/down helps with this) and so making sure they are firmly taped in place is important. I use Tegaderm film over the whole thing, which my GP supplies.
I also remove the transmitter when it says the sensor is up and recharge. I do this by having a special pair of tiny, very sharp scissors, and I cut round the transmitter very carefully before pulling it from the sensor, making sure I hold on to the sensor.
The sensors are not okayed for being put in the leg, but I find the leg and arm are the best place for them - your torso twists and stomachs are very movable things. in fact my last few sensors have lasted through 12 days and one longer than that by being situated north south on my arm, removed and recharged before being put back and firmly taped again.
I also remove the transmitter when it says the sensor is up and recharge. I do this by having a special pair of tiny, very sharp scissors, and I cut round the transmitter very carefully before pulling it from the sensor, making sure I hold on to the sensor.
The sensors are not okayed for being put in the leg, but I find the leg and arm are the best place for them - your torso twists and stomachs are very movable things. in fact my last few sensors have lasted through 12 days and one longer than that by being situated north south on my arm, removed and recharged before being put back and firmly taped again.