The cache is NOT at the posted coordinates. Solve the puzzle below to determine its location.
Just north of Terilbah Island are two small islands resembling a pair of spectacles, each having a clump of vegetation in the centre surrounded by open silt rimmed by a sandy shoreline.
Both are officially nature reserves and off-limits to caches, so the cache is somewhere on the adjacent shore at the water's edge. But when I looked at my notes, all I could see was a blur of indecipherable numerals so perhaps it's time to visit an optometrist.
"Look at the eyechart on the wall and tell me what you can read," he said after dimming the lights.
"That's not good, is it?"
"It's nothing we can't fix. You have geocacher's long-sightedness, meaning you're okay navigating towards the cache until you get close, then you lose your bearings. The degrees and whole minutes are fine but those decimal minutes are just a blur, am I right?"
"Exactly."
He swung the lens mounting arm across in front of my eyes and began making adjustments. "That should just about do it. Can you read the bottom line now?"
"Um, A N O T H E R F T F C H A M P. Wow!"
"Excellent. I'll prescribe the new lightweight lenses with a refractive index of 1.74, a 1mm thickness and a positive meniscus. For your south-facing eye the outside radius of curvature is 0.4500994 metres and the inside radius is 0.799174 metres, and for the other eye those radii are 0.627827 and 0.701167 respectively. Convert those to the lens power in dioptres and you'll have your lost cache's decimal minutes."
"How do I do that?"
"Just look up the Lensmaker's Equation. If you do your sums right, both should yield positive numbers between 0.1 and 0.9. Don't forget to convert the lens thickness into metres."
Although I used my kayak when placing the cache, I ran aground a couple of metres from the shore and had to wade over, so this one is probably easier to do starting from the land if you don't mind getting your feet wet. I've rated the terrain accordingly.
My thanks to lee737 who 3D-printed the containers for this series.