Hi @Kelvin12 You need an accurate scale (milligram resolution) to measure out the 1 gram of pure NaCl and an accurate measure for the 1 liter of distilled water, make sure the salt is throughly diluted and ideally making sure the solution is at room temperature when you measure. If both probes comes out close to 100 ppm I suspect the solution mix is off, so I wouldn't toss the probes just yet.Thanks Michael I bookmarked you recomendation, currently out of stock but will keep on it.
I tried your salt mix and came up with these way off readings, 137 (old meter ) and 106 (new meter). Obviously not good so both are heading for the bin. .