19/03/2026
You might recognise this test for colour vision. 1 in 20 males have colour vision deficiency. Around 1 in 2000 females do too. This book helps diagnose. People with normal colour vision tend to see 8 and 29. The others see 3 and 70 usually.
Very occasionally when i ask "what number do you see here", a young person would say 2 and 3. Never an older person though.
You can see why in the comments.