that is your current True heading being displayed, but u can change that to your liking to PPOS on the IRS display selector knob to "fill the box". this was done i believe because a lot of the fellow simmers wanted a bit of realism with the IRS as it set automatically within a minute before 4.3. with this we atleast have a little bit of control, but i could b wrong and this may only be a workaround. :)