Caves, sinkholes and other karst features generally have very different electrical conductivity properties than the surrounding limestone bedrock. Caves and caverns that are filled with air are highly resistive relative to limestone; water-filled caverns are highly conductive relative to limestone; and buried sinkholes filled with clay are also highly conductive relative to limestone. Geophysical survey of potential construction sites in limestone terrain is an effective tool to locate these and other karst features that pose engineering challenges.
I’m a new jailbreaker too, but I experienced this link while looking to jailbreak an old Iphone-4 to check things out before jailbreaking a tool that I rely on. It appears to me enjoy it’s either a link, the “up arrow” is of artwork that VO does not study, a few type, or it was never a real jailbreak in the first place. That said, it wouldn’t benefit your device anyway as it is made for another IOS version. Jailbreak tools are created to use security holes in each distinct IOS model and device, which means you have to look for anything created for IOS 10.2.1 and the iPhone 6. The Yalu jailbreak software was just released, and Iam pretty sure your device is covered by it.