UPDATE: As I have not been maintaining this app for years, I've decided to make it open source under the GNU General Public License v3.0. If someone is interesting to become a maintainer or a contributor, send me an email.
The full source code is now available on GitLab: https://gitlab.com/razorscript/fxcalc

The app was built with Adobe AIR SDK and the Feathers UI library. Both are now quite outdated. It would probably take not too much effort to update the app to use a recent version of AIR SDK from HARMAN (the current maintainer of AIR).

FXCalc is an accurate formula scientific calculator with a modern look.

Enter a mathematical expression and use the equals button to evaluate it, carrying out calculations in sequence determined by common mathematics order of operations.

Note: The app is fully free and doesn't have any ads.

The expressions and their results are stored in the calculation history. To go back and forward in history, use the up and down arrow buttons.
To start editing the displayed formula, use the left or right arrow button. When editing a formula, use these buttons or tap anywhere within the formula to move the caret.
To clear the current formula, use the AC button. When viewing a formula, you can also just start entering a new expression without clearing the old one.
To switch between the insert and replace modes, use the INS toggle button.

The calculation results can be displayed in different formats.
To display results in normal (fixed point) notation, use either Nor1, Nor2, or Fix buttons.
To display results in scientific (exponential) notation, use either Sci or Eng buttons.
To adjust the number of digits to display, long-press the button (except Nor2) then use the slider.

The angles (e.g. for trigonometric functions) can be expressed in either Degrees, Radians or Grads. To cycle between angle units, use the DRG button.

To access the hyperbolic and inverse trigonometric functions, use the hyp and inv toggle buttons.

Currently, two variables are available to use, additional variables will be added later.
The answer variable (Ans) is a special variable that contains the result of the last successful calculation. To recall it's value, use the Ans button.
The memory variable (M) is a general purpose variable with dedicated buttons
To set, recall and clear (set to zero) the memory variable, use the MS, MR and MC buttons.
To increase or decrease the value of the memory variable by the current value, use the M+ and M- buttons.

The display precision is limited to at most 12 decimal digits, the decimal exponent range is limited to [-99; 99].
Internally, the calculator uses IEEE 754 double precision floating point arithmetic, allowing representation of numbers with a decimal exponent range of [-308; 308] with 15–17 decimal digits precision.

Bug reports, feature requests and other suggestions are welcome. Don't hesitate to contact me.

If you'd like to test the latest features early, join the beta program:
https://play.google.com/apps/testing/com.razorscript.FXCalc