Well his meter only reads to 1990 so he's going to have a hard time calibrating it to 2190.

If it's the basic meter i'm thinking of it reads at a 0.7 conversion scale and is calibrated by sticking it into "something with a known tds number" or what not and calibrated to that. I don't see anything on mine that switches to a 0.5 conversion and nothing in the instructions either so I'd be interesed to know if that actually works although I doubt I would change at this point because I'm really used to the 0.7 now.

Meters that read e.c should be calibrated with a conductivity solution instead of a tds solution (at 0.7 conversion I use 141.3 solution)
Weedhound Reviewed by Weedhound on . TDS Meter Calibration Issues I'm hoping that there are some really smart folks out there that can help me understand something of the world of meter calibration. After making my purchase of an Oakton TDSTestr11, I asked the young genius behind the counter for an appropriate calibration solution, for which he hands me General Hydroponics Standard Calibration Solution. Here's where the confusion starts, as the package indicates that it calibrates to 1500ppm (NaCl), 2190ppm (442), and 2930S (microSiemens). So everything Rating: 5