Use RunCal to solve mathematical equations. RunCal is an RPN Calculator. In Reverse Polish notation the operators follow their operands; for instance, to add 3 and 4, one would write "3 4 +" rather than "3 + 4". An advantage of RPN is that it obviates the need for parentheses that are required by infix (common) notation.
Calculations occur as soon as an operator is specified. Thus, expressions are not entered wholesale from right to left but calculated one piece at a time, most efficiently from the center outwards.
The automatic stack permits the automatic storage of intermediate results for use later: this key feature is what permits RPN calculators to easily evaluate expressions of arbitrary complexity: they do not have limits on the complexity of expression they can evaluate.
Brackets and parentheses are unnecessary: the user simply performs calculations in the order that is required, letting the automatic stack store intermediate results on the fly for later use. Likewise, there is no requirement for the precedence rules required in infix notation.

Example 1: If you touch the buttons "2; Enter; 4; /" it will properly show the resulting value of 0.5.

Example 2: Touch the buttons "3; set x; C; 4; set y; C" to set the values of variables x and y. Then touch the buttons "x; x; *; y; y; *; +; sqrt". It will show the result of the equation sqrt(x*x + y*y), that is 5. You can reset the values of variables x, y, z anytime.