How to use it:

Input the number using the phone keyboard and virtual "keys" ( . , +/- , Exp ) on the display (use arrows and OK button). The calculator starts with an "empty string". If one wants to enter zero he/she must press the key 0. If there is no exponent, +/- changes the sign of the whole number. Whilst the exponent is inserted, +/- changes the sign of the exponent. CE clears (only) the displayed number. The whole session can be reset by the Soft key Clear (but it does not affect the memory and the deg/rad flag). deg ( rad ) shows the current angular measure and enables to change it. 

Calculator offers basic operations, powers, trigonometric and inverse trigonometric functions, logarithms, memory, etc. At the end of the "virtual keyboard" there is a couple of unit conversions (Anglo-Saxon vs. metric). The calculator applies priority rules as follows (from the highest to the lowest priority): functions and the equal sign (=), the power (xy), multiplication (×,÷), addition (+,-). Intermediate results (together with the signs of current operations) are shown above the main window. 

MR enables to read the content of the memory if it is not empty, mr indicates an empty memory. Memory can be erased by inserting an empty string by >M. Conversion to deg., min., and sec., dms, depends on the state of the deg/rad flag. It can convert radians to degrees directly. If one exits dms by pressing O.K. the original (input) number is retained else (Clear) the session is reset. 

The input for trigonometric functions is restricted to the interval from -300 to 300 rad (-17188..17188 deg). In case of the power, x^y, if x is negative y must be integer. Relative precision of trigonometric functions on the interval -2p..2p is better than 10^-7. Relative precision of inverse trigonometric functions and logarithms is about 10^-7. In general, one can confide in 5-6 valid digits. The results of calculations are non-editable (in fact, the sign can be changed, digits added, etc. - but these are just "side effects" of the method used). Minimum nonzero positive number is about 10^-38, maximum number about 10³⁸. But it is not recommended to use exponents above 15 (below -15). The only exception concerns logarithms - they can handle large exponents. Maximal input number for exponential function, e^x, is 88, for factorial, n!, 34.