That is not 75%, it is 0.75%. - as @Batman said. 

According to other sources, it is already too late to change the chain. (Than what the purpose of this tool? - would be the next question)

From wikipedia : "Twenty half-links in a new chain measure 10" (254 mm), and replacement is recommended before the old chain measures 256 mm (0.7% wear)"

What does chain worn indicators 75% mean?
I was watching Scorpion (VOY) parts 1 and 2 last night and a thought struck me: sure, their computer interface looks pretty cool, but why do they have a physical interface (i.e. they tap the screen physically) in the first place?  It's made quite clear that they can interface with each other through mental transceivers and they make a big deal about thoughts being a more efficient communication method than verbal communication in Scorpion Part 2 with Tuvok and Janeway.  Therefore, wouldn't a mental interface with a computer be more efficient?  Surely, then, they could have the drones in their stations for most of the time, just thinking to interact with the computer rather than having to tap their way through an interface.  Is there any reason given for this?

And, although I only recall seeing 7 of 9 using the computer via physical interaction in Scorpion, there are plenty of instances in other episodes where other drones also use physical interaction with the computer.
