Personally, I would make the input a string control. Right-click the control and select "update value while typing." Then use the value change event. Convert the string into a DBL and do the calculation in the event. This way you don't have to worry about key focus and the flicker that occurs when you type in the box.
Using the Abort button to stop your VI is like using a tree to stop your car. It works, but there may be consequences.
