Well, actually, I can damp out the noise in 2 ways. One is by using an analog meter. Then the inertia of the needle damps out digital fluctuations (another benefit of analog). The needle simply does not move fast enough. Another way is to ballast the circuit by using 2 1.5 V AA batteries and a pot and center the reading on zero. In the mv range, and with such low current, the system is hypersensitive. Waving the probes in the air can give me readings varying from -100 to +100 mv sometimes, but it varies with the phase of the moon.
At EK we used some sort of custom amplifier and lots of grounds to prevent this type of noise. At home, I am just improvising. Unfortunately, I never knew the contents of the black boxes we used.
Another part of the noise is the conditioning of the Silver electrode and the cleanliness. We "bought" our electrodes prepared for us, and then conditioned them with standard salts and used another black box. Again, I am improvising as I go along.
I should mention that there are 2 types of noise, if you read into the above what it implies. There is a rapid fluctuation back and forth and a slow drift up or down. The former is due to the low current and voltage, and the latter is due to conditioning and deconditioning of the electrode.
There is another separate problem, and that is with my Potassium Nitrate. It is not pure enough and tests positive for a tiny level of KCl in it. This affects the action of the bridged system during long use. It is used very dilute though, which reduces or minimizes the effect of the impurity on the system during measurement.
However, purchase of pure KNO3 is restricted in the US at the present time. So, I have to use what I can get right now.