Thanks, I am glad you like it!
I actually thought about adding this. But I wasn't sure what to consider an entry as the expression is evaluated every keystroke. With the command it is when you press enter. But in GUI when you type an expression you can have many valid entries which can clutter the history.
For example, while typing 35 - 24 * 22 6 entries will be valid: 3, 35, 35 - 2, 35 -24, 35 - 24 * 2 and 35 - 24 * 22. I guess we can drop the first two as it is only a single number.
I guess it could be a valid expression when the window is closed.