Dr Ishihara's Puzzle
Have you ever looked at all those spots on Royal Oak roundabout and have it remind you of anything? To me it looks like one of those tests you take to see if you're colour blind. So the theme of this puzzle is just that.
Most people will find this puzzle as easy as looking at the pictures below and finding the numbers. However, for as many as 8% of men and 0.5% of women of Northern European ancestry, they may find this is a very challenging puzzle and need some help to solve it. That's because they may have a form of colour blindness.
There are three main kinds of colour blindness, based on photopigment defects in the three different kinds of cones that respond to blue, green, and red light. Red-green colour blindness is the most common, followed by blue-yellow colour blindness. A complete absence of colour vision —total colour blindness – is rare.
A common way that colour blindness is determined is by taking an Ishihara test. The test was named after its inventor, Dr Shinobu Ishihara, a professor at the University of Tokyo, who first published his tests in 1917. Simply examine the Ishihara test plates on the cache listing page. Sit approximately 75cm from your monitor with the circle at eye level. Preferably have natural light with no glare on the screen. Artificial lights and glare can affect the colour of the circles. If you have no form of colour blindness you should have no difficulty making out the numbers on the plates.
The last two plates are included to show the coordinates to people with the most common form of colour blindness. People without colour blindness should not be able to easily pick out the numbers in the plates.
The cache can be found at S 36 55.ABC E 174 46.DEF
People with the most common form of colour-blindness should be able to pick out the correct numbers on these two Ishihara plates. People without colour blindness should not easily be able to see the numbers.
| South |
East |
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Check your final coordinates (if you must - it should be obvious what they are), for a hide hint, although it's difficulty one so you might be able to guess how it's hidden!
