My Desire calculator calculates incorrect

RealCalc is my favorite, because it looks (and functions) exactly like the scientific calculator I used at school!

 

I have always used Retro Calculator.

 

Calculator by Stormin Dormin works good.

 

Strange. I just tried that calculation on my Desire HD and it gave the same result! What's happening there?

 

Same result on my Sprint Evo!

 

This is most likely because the calculator isn't using enough internal precision (that is, the right type of variable for floating-point math; possibly a float where a double should have been used).

The thing is, computers love numbers but inherently suck at decimals.
You know how you can express "1/2" quite perfectly as "0.5", but for "1/3" you get the problem that "0.33333..." is never going to be entirely accurate? The same thing happens in binary, only on different occasions.

So when you hit one of those occasions, you will see a precision error in the form of a number that is "ever so slightly" smaller or larger than you'd expect.

Wikipedia: Representing_fractions_in_binary gives the following example.