Hey Jason,
The problem is that a new electrode is rehydrating to some extent, even though they are packed with a preservative solution on the tip, it will need to rehydrate to get better readings. The most accurate results are obtained by placing the new electrode in water for 24hrs, then calibrate with 7 rinse in distilled water and wipe down, then calibrate in 9 and repeat one more time. After 24hrs in water and following this procedure the results should be very accurate and very stable. As the electrode ages the time in each calcibration fluid needs to be extended, a fresh electrode should be stable in it's reading in about 1min, an old electrode may need to soak for 5 minutes, Imagine an electrode is a battery (it is really just a fancy battery) it is putting out about 100mV, as it gets old the battery starts to die and the readings are off.
