LeoCalculator is an application for performing calculation of mathematical expressions that could include not only basic operations but also functions and brackets. Edit box "Expression" has to contain a string of mathematical expression that is supposed to be calculated. It can contain: numbers in with or without decimal point and with or without a power of 10 like 1.2e-2 or 3.E3; pi in this application is equal to 3.141592653; basic mathematical operations +,-,*,/; power of grade operation ^ used like 2^3 = 8; brackets determining order of operation execution; elementary mathematical functions: sin,cos,tan,asin,acos,atan,ln,log10,exp,pow10,abs,sqrt; basic statistical functions as sum, mean, sigma (standard deviation) student and trust for calculation probability and trust interval. Arguments of the functions have to be an expression surrounded brackets; Variables can be declared and edited separately from formula and can be any combinations of letters and numbers without spaces and reserved words: value expressions as usual are numbers but in most cases it could be mathematical expressions too.