TDS meter calibration checks

[J and S]

How do you guys check the accuracy of your TDS meters?
I have 2 abd the new one is showing different tap and pure readings to the old one.
My suspicions are that the new one is wrong showing tap water at 063 when it used to be around 90 and pure at 009 whilst the old one shows 001 for pure.

 

[Chris33]

Google tds calibration solutions and all shall be revealed

Sent using the http://Window Cleaning Forums mobile app

 

[J and S]

Yes I know about calibration fluid but one of them is only 2 months old and is all over the place and I wanted a quick fix.

But that won't be happening now because the new one I bought looks as though it's a from a faulty batch.

There is no calibration screw on the back.