Rick Hughes wrote:

I bought a pH meter which is aimed at gardeners ...
http://www.amazon.co.uk/Gardman-Soil...1P3XAEE/ref=sr
_1_3?ie=UTF8&qid=1347222580&sr=8-3

I thought I could also use it on liquids ... but I have serious doubt it
is reading acidity correctly.
Is there a simple way of testing ?

I think it's RTFM time. I had one of those some years ago. They are not
very good. As I recall the instructions state that they will not work
with solutions they will only work when rammed into the soil. They are
not proper pH meters which have a porous glass electrode, they work on
the voltage generated by the bimetallic tip when in contact with soil
and apparently that will not work properly in a liquid.

At the time I had access to a lab with a proper pH meter and the Gardman
types produced very odd results when used with pH reference buffer
solutions.

Short summary, the Gardman and similar "pH meters" are about as much use
as if they had been made from chocolate.