Quote Originally Posted by Ian Grant
That's always been the way here in the UK

1+9 = 1:10
1+1 = 1:2

It's far less ambivalent

Sorry, but 1+9 is not equal to 1:10.
1+9 is 1 part of liquid added to 9 parts of other liquid. 1:10 is one part of liquid added to 10 parts of another liquid. In reality, photographic solutions should be expressed in percentages. IOW, a 10% solution by volume would be 1+9, but not 1:10.

So for example mixing Xtol at 1:2 is adding 1 part of Xtol concetrate to 2 parts of water and this in effect is a 33.33% solution.