Get 100 as an answer with only four keystrokes on a regular calculator.
All other than the aforementioned two keys.
Atleast two operators must be used.
On my actual junky little calculator, these four button presses give 100:
In fact, any non-zero digit will work. Calculators will just use the current value in the display as the operand if you didn't type a new one, so what you're doing is saying: Start with $1$. Divide it by ... (the still displayed) $1$ turned into $1\%$, or $0.01$. Then hitting $=$ gives the answer of $100$.
Also, try it here:
which behaves the same way.
I found another solution.
.1 first and second key, 1/x third key, x2 fourth key. You need a calculator with those buttons though.
The OP says that calculator is just for reference, meaning I can use "a regular calculator" that's slightly different? It's the standard calculator that came with my windows 10.
You can do it with 3 mouse clicks on a virtual claculator (Windows or Mac):
With the calculator in "programmer" mode, base 16 selected, click 6 4 "base 10"
And for the pedants that require 2 "operators":
With the calculator in "programmer" mode, base 16 selected, click 6 4 "base 10" =