Dynamically Updating Characters Typed

I have a form, very basic.. it contains more or less an inventory frontend in which users input computer equipment that we carry in our state dept.

To make this very brief, in my form at the end I have an "Additonal Information" textbox in which users can add additional notes, comments, etc.

As textboxes are constrained to 255 characters, I chose to show an additional textbox directly below the Additional Information textbox, with a control source set to =Len([Additional_Information]) to show users how many characters they have typed.

What I'd like to do though, is make this value dynamically update while the Additional Information textbox is still in focus... so far, all I can get it to do is update once a user has tabbed away from the additional information textbox.

Is there a way to make this update in real-time?

I appreciate any feedback at all.. thanks :)