The options window can be found by choosing Options from any menu or by using the Systems Information button (i ) on the Modes Panel.
Show Intro Splash toggles showing the introduction (splash) window when starting the Expression Calculator
Save Settings on Exit toggles saving the Expression Calculator's window position and size when terminating the calculator. Starting the program again will not restore the last known position and size if this option is unchecked.
Constraint Screen Limits option forces the Expression Calculator window to be bound to the desktop size. If you use multiple monitors, you should disable this option.
Direct Mode calculation enables typing an expression and linking it to the previous result if it starts with an operator, like any standard calculator. For example, evaluating 2 + 2 results to 4. Evaluating + 2 will add this to the previous result, producing 6.