simple enough..

:caddy:HUD is data
displayed on your windshield by projection that you can't see if you're
wearing polarized sunglasses.

Originally this capability was designed for use in fighter jets, although
it's available in some commercial airplanes too. It was offered as an
option in the '05 Caddys.It displays speed, rpm and even GPS info.

Many Corvettes have it. People with it generally love it.

I have it in my 02 Bonneville SSEi. With out getting into details, I think it's over-rated. I won't go out of my way to get it on my next vehicle.

I loved it on my C6. If I would have ordered my STS new, I would have checked the box. It's really cool IMHO.

I also have it in my C6 Corvette and really like it. I wear polarized sunglasses, and can still see the HUD display perfectly. It does make it difficult to see the HVAC and radio display though.

We have one STS without it and one STS with it. I can tell you that once you get used to it, you really miss it in the other car. It is VERY well done in the STS and shows you all kinds of things.

To me it is a really nice feature.
The meaning of "head up" is that your head is always up. You need not look down at the IPC or radio (on some cars) to see how fast you are going or other important information. Such as how fast you are going when you see that cop car!
There is usually a screen in the dash paired with a special windshield that reflects the image back to you with the data that they have decided you need.
Some HUD displays have different adjustments and changeable parameters depending on what information you want to see. You merely have to briefly change your focus to see the data on the screen and then refocus on the road without moving your head around.

It is usually a fairly expensive option.

I have trouble driving cars that do not have HUD.

I had a HUD on my C5 Corvette and really liked it. My in-laws have it on their Buick Rendezvous but I can't see it because it doesn't adjust high enough for me to see the image projected on the windshield.

:horse:

i had one on my 06, but now i have the v which didn't offer it. i miss it alot. one thing to think about, is if you have the nav, the turning directions,etc, are also displayed on the hud. very cool.

as far as polarized glasses, i found it to be true with the sts, but as stated by someone else, i can see perfectly with polarized sunglasses on my c6...weird. i'm told the windshields are diff.

IS it possible to add it extra if your sts didnt come stander with it?

i've been told "no", but i'm sure anything can be done if someone is willing to try hard enough.

It would require extensive modification and big money in parts. I am not even sure where you would get them.

This is one of those things that would be better if you sold your car and bought a used (or new) car with the equipment already installed.