ive been brewing my own colliodal silver for months now and even with the meter 
to measure the ppm of it i allso monitor the vairious voltage outputs of the 
constant current circuit i use and  been doing this alot and have got to the 
stage where  i can determine the ppm by the voltage outputs and i even use the 
ppm meter to confirm this.  for the size of the jar and the amount of water and 
the amount of electrode submersion all helps ,