It sounds like you're not "setting" or storing the values between the 7.0 and 10.0 solutions. If the readings are too close to each other, the calibration will fail. First do the 7.0. Let the numbers stabilize. Then "select" to store that reading. Rinse the probe then repeat with the 10.0 solution. Again, when the numbers stabilize, "select" to store the high reading. Then calibration is complete. Rinse the probe again and you can now put it in the 7 or 10 solution to see if it actually reads 7 or 10.