Make sure you are aware of and you check your calculator settings. You just never know when the calculator gnomes will sneak into your room and switch it from radians to degrees. You'll be further mystified if they find the "GRADS" setting.
On my financial calculator, it has setting for "End of Period" and "Beginning of Period". One must select the correct setting to get the right answer. Personally, it does not matter how many times I have hit those buttons, I ALWAYS reset for the value that I want - always!
Never leave it to the gnomes!