[Shaun_Ashmore]

How do you calibrate them?

Shaun

[Mike Osbourne]

With a calibration fluid.

Try scientific equipment suppliers.

[derek west]

i'd guess with distilled water. but ive never used one so not sure if you have to calibrate at the end of each scale or the middle will do.
derek

[Dennis]

I had one a few years ago and it was check and adjust ph7 and then ph4
If near enough is good enough and you have them Prochem Fibre Shampoo is 7 and Fibre & Fabric Rinse is 4. 

[Roger Koh]

I had one a few years ago and it was check and adjust ph7 and then ph4
If near enough is good enough and you have them Prochem Fibre Shampoo is 7 and Fibre & Fabric Rinse is 4. 

What a brilliant idea!

And when you run out of Fibre Shampoo, use blood with a universal pH value of 7.4 wouldn't be very far wrong too! "LOL"

[Mike Osbourne]

Roger

Knowing this lot, you would have better chance with a stone. 

[Roger Koh]

A stone without a rope makes no sense