Most of the A/F gauges out there are simply glorified voltmeters. Unfortunatly most of the O2 sensors in production cars do NOT have a flat response curve - they peak at 14.7:1 A/F. This is NOT where you want to tune your car but it's wonderful for emissions. Here's what it's response curve looks like
It IS possible to change the stock response curve of many A/F meters like the Autometer units so that they're more sensitive in the ranges that are most interesting and so that they don't give you a disco lightshow at stoplights when the A/F is constantly being adjusted in closed loop. This site
does that for a fee. Been awhile since I'd been there but I looked it up just for you. It seems he's now selling digital gauges now too
I guess if the market demands it... Oh, and stock O2 sensors don't exactly have really fast response to changing conditions - another not good thing when you run into "Oh Sh*t" territory..
To get accurate readings you need a wide band O2. These are now being used in some Hondas and LEV rated vehicles. However you need a box to interpret the output into a smooth response (1-5volts) and the sensors themselves cost over $100 (add-on box is $400+). Until just tonight I was hearing prices about double that and I've not bought one myself so take that FWIW. At least prices are coming down - it used to be that WB O2s were like lab equipment. VERY expensive, limited lifetime, couldn't survive lead, had lifetimes measured in hours, and had to be calibrated
These new ones have none of that and can even stand leaded race fuel to a degree
For further reading on the subject I suggest a visit to this site
which discusses EFI and O2 sensors in pretty broad terms. Do note the MUCH flatter and wider range of the WB sensor. I put little if any stock in those A/F meters, I have one for a carburated car but I've not yet bothered to hook it up due to it's low value as a real tuning aid...
P.S. The TurboBuick forum in the EFI section is where the F.A.S.T EFI guys hang out and there's some VERY good tech in there if you read. A Holley engineer hangs out on Chevytalk's EFI forum and also dispenses good advice on EFI. HybridZ has some too but we're not up to the level of the other two forums