You dont need to use reference button to alling your INS.
When you start up the VIGGEN, leave your NAVIGATION SELECTOR in EBR mode, dont switch on your HUD. When you are on runway and well alligned with it, switch to NAV mode. Run up with stage 2 and when you reach 250km/h, your INS system alligned it self.
If you land (after your mission) and you have to take off again, repeat these steps but, in this case, you have to use the reference button(when you're in the center of the runway) because INS system alligned it self just one time.
P.S.: sorry for my bad english...