Basic math calculators

• Mathematically impossible operations (such as attempting to take the square root of a negative number) will generate a warning notice (this calculator only deals with real numbers).
For addition, subtraction, multiplication, and division the calculator works
in a simple RPN mode. Enter the first number in the Xvalue edit field,
hit 'return' and enter the second number, and then hit the '+', '', '*',
or '/ ' key. Note that for performing subtraction in RPN, the ‘_’ (underline) key is substituted for the '' (minus) key. The result appears in the Xvalue field. Also note that when computing sines, cosines, or tangents, the calculator expects angles in degrees (not radians). 
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