When calibrating a pH electrode, the user is mitigating the effect of the condition of the electrode, among other factors. pH electrode bulbs have an inner and outer hydrated gel layer that contributes to the observed potential of the sample. Once the electrode has been calibrated, the specific potential resulting from variances in the outer gel layer has been mitigated. The physical properties of the outer gel layer will be modified if you touch the pH electrode. If this occurs, the calibration needs to be repeated.
If you are calibrating several electrodes in the same buffers and are concerned about diluting the buffers, you can use the corner of a Kimwipe or similar tissue to gently blot off the drops of pure water used for rinsing the electrode.