Supposedly it tricks the AP into thinking its in Cat II mode even though its not. I've never tried it but supposedly it makes the AP "smarter" and fly the approach better. The only problem I see with that is that the Honeywell seems to have the most problems when you are far away and they are crossing airplanes in front of the LOC antennae, something that would not happen in Cat II conditions so I'm not sure how it would handle those situations.