Hexadecimal arithmetic on calculator (casio etc.)

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When I do hexadecimal subtraction say, 2A-324 on a casio calculator or any calculator in general, i get the result as FFFFFD06

Why do i get so many F's ?? dosnt F stand for 15 in hex. In any general arithmetic, how many digits should i consider for the final answer, say in a subtraction operation in which the bigger number is negetive (324 in my example).

Is my answer only D06?

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You get this result because the calculator uses only 32 bit arithmetic in this case, i.e. it actually computes $\mod 2^{32}.$ $$2A_{16}-324_{16}= -2FA_{16}$$ $$2A_{16}-324_{16}+ 2^{32}= FFFFFD06_{16}$$