Cheap TDS pens

[Hydrophonic]

Anyone have problems with cheap TDS pens? Tried testing a couple in conductivity standard of 2.76mS, but the both are in PPM and display about 1000ppm. Is this correct? The manuals say they have a conversion factor of 500. Does this mean that they should display 1380ppm in 2.76mS standard? Am I missing something?
They're both cheap Chinese units from eBay and neither has a calibration screw to adjust it... Should I just get a refund?

 

[Major PITA]

With a 500 conversion (NaCl type), 1ms = 500 ppm, so "Yes." 2.76 ms = 1380 ppm.
Not sure what the problem is. Mine is one of the cheap HM Digitals and works well.

 

[Hydrophonic]

Ah ok, thanks for the clarification!

Odd that they are both out by the same amount. Perhaps the conductivity standard is incorrect...