Yes, an accounting system than I made, where needed a calculator
what I make is a simple one:
Put a textbox for input values
Put a textbox for show results
Out a command button to process the calculation
Put a command button to cancel
On Calc button get the calc operations from textbox, verify than is a valid expresion and do an Eval() function and show the result
The valid expresion is for allow only valid expresions and avoid to user input a VFP command or missuse the calculator.

Advantages, full control over the expresion, grouping values with (), use of internal functions like sin(), cos(), abs(), etc...

Just my solution

Mauricio