Monty,
All Ishihara 24 plate tests are the same.
The pass/fail all depends on the pass criteria
i.e. how many mistakes are allowed.
I believe the makers of the test specify something like up to 5 mistakes as 'colour normal' and award a pass. Someone correct me.
However, the aviation authorities, in their wisdom, usually reduce that number.
UK CAA - zero mistakes = pass, otherwise fail.
AUS CASA - zero mistakes = pass, otherwise fail.
USA - I think a few mistakes are allowed. Someone correct me.
I suspect the truth is that 'colour normal' is not a specific thing but means 'within a tolerance'. I also suspect that the Ishihara plates can weed people out within that normal tolerance if the allowed number of passes is less than the makers allowed number of mistakes.
Its all bull**** - join the CVDPA.
Last edited by outofwhack; 13th Jun 2012 at 14:53.