Your logic's right Vaugh

A ratio of 1:1 meands life size in our case FS - Full strnght - as no dilution (or concentration) is taking place, 1:50 is a 1 part in 50 there's no ambiguity with that. 1+49 means the same as 1:50 but 1:49 means one part in a total of 49.

What is a ratio like 1:1 or 1:50 it's well written about and not contentious either, see Dilution ratios.

Ian