Bacause CS has caused considerable frustration with me regarding ppm, may I come in here and relate my experience with meters and the CS I produce using my own CS generator. I have a 'need to know' mind set with regards to what ppm I am producing and I can't be without a meter, (I have the one JAB mentioned as well as another one). While meters are necessary, [my opinion], I used to get frustrated to the max because my readings would change with each test I used to do. I believe I now understand, (after bucket loads of research and asking here), that it takes my solution around 24 hours or so to stabilise and give me a consistant reading. I would monitor and test ppm during the production process and do a final test on completion, (at my desired ppm), but when I tested it again 4 or 8 hours later it would be lower, and lower again up to 24 hours or so, after which it stabilised and remained unchanged.
On research I have done the reason for this, well in my case anyway, is the fact that MOST of the silver in my solution is in 'ionic' form as compared to 'particulate' form and it takes 24 hours or so for my solution to stabilise after some of this 'ionic' content agglomerates, (or 'sticks' to the silver particles which are already in my solution to a lesser degree), to form more particles, thus my meter reading would drop initally over a given amount of time. Water temperature will alter readings as well. After the said 24 hours or so it stabilised which says to me that only then could I say that my solution was "x" ppm. But, my opinion is that this is only the 'ionic' content which means there is actually more silver in particulate form of which the meters will not pick up. So if my solution is "x" ppm on the meter reading, I can assume the TOTAL silver content is higher after these aforesaid 'ions' have agglomerated to form more 'particles' so I am satisfied that my Colloidal Silver solution is then 'AT LEAST' that "x" ppm on the meter. The 'ionic' content will be lower, (on the meter reading), as the 'particulate' content increases before stabilising. I state this because I had a lab test done several years ago, when first learning about CS, and the result came back as..."x amount soluble with a slightly higher total silver aggregate". This, to me, means that the 'x amount soluble' is the ionic content and the 'slightly higher total aggregate' is the particulate content.
This has been my experience using my generators. I can't speak for 'shop bought' generators though.
I only come in here in case others have had their heads screwed by 'differing' meter readings and to pass on my experience with the solution I produce in case it is of any interest. Maybe my 'mind set' is causing me to be too meticulous but I am not content with 'guesswork'.
I am by no means an expert with CS but this is what I have worked out over time, talking on here, and doing my own research, and of course I will stand to be corrected if necessary. I'm learning all the time.