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Learn how GPS works maybe? It's not a two way protocol, you can't "deny usage" to anyone, the satellites are just blasting out coordinate numbers to everyone. It's up to the receiver to decode positions from it.
GPS denial can be done in several ways: 1) Jamming - GPS signals are very weak to begin with and can be jammed by various techniques 2) Restricting the civilian codes (there are separate transmissions for military use but the US can deny/degrade access to the civilian ones)
Here are a couple of proof-of-concepts... (obviously you need a compliant browser to view this)
HP calculators have always been hackable.
The reason that the 12C / 12C Platinum is allowed on exams (e.g. CFP and CFA Certification Exams, and the GARP FRM Exam) is precisely because they are deemed "not hackable" by the people running the exams.
I guess professors today are a bit more savvy, but when the HP28 first came out and I asked my history professor if I could "bring a calculator" he couldn't see why not
There is hardly a thing in the world that some man can not make a little worse and sell a little cheaper.