OK... here's a quick write-up on some SGII tips and tricks.
The math may get a bit fuzzy, but I'll try to clod trough it. There are two settings you can set, one is Speed plus or minus whole percents (±1%, ±2%, ±3%...). This effects MPH, DIST, MPG, DISTANCE TO EMPTY (think that's it). So if you see that SGII is reading too low on MPG, DIST, or MPH, then bump up SPEED, till MPH on the gauge and on the dash match (or until DIST on the gauge and on the odometer match).
The other setting you can adjust is in FILLUP and that controls how it monitors fuel use. This is a plus or minus percent meant to get the gallons you put in the tank to match the gallons SG calculated you burned. This effects GPH, MPG, DIST TO EMPTY. So if SG has calculated that less gas was burned than what you just pumped in, the set calibration to some positive percent till they come in line. The manual
(search fillup) goes over this to some detail.
Now the interesting part comes when you start comparing your MPG. Since for me the MPG is the most important figure. MPG is Miles/gallon. Another ratio to state it is MPH/GPH (GPH=gallon per hour).
So increasing MPH increases MPG.
Decreasing MPH decreases MPG.
Increasing GPH decreases
Decreasing GPH increases
Sounds simple, but it's easy to get mixed up. So if SG reports a lower MPG than we calculate (either at the pump or on the FCD) then we need to increase MPG. We can do this by either increasing (+%) the speed calibration or decreasing
(-%) the fillup calibration. And conversely if SG reports a higher MPG than we calculate (either at the pump or on the FCD) then we need to decrease MPG. We can do this by either decreasing (-%) the speed calibration or increasing
(+%) the fillup calibration.
Confused yet? I've added a spreadsheet to the uploads section to do the math for you.
ScanGaugeII Calibration Worksheet
Now there is a little trick I found on the FILLUP calibration. I found it best to do FILLUP>DONE without calibrating, then when gallons consumed is 0.0 do FILLUP again (before you start the car), that way you can set the calibration in arbitrary tenths of a percent 1.1%, 1.2% ... etc. Try it on your next tank to see for yourself.
If you have more than one SGII and want multiple TANK (ie trip) totals, or multiple CURRENT totals, you can hook them up to each other. This is also a nice way to see the trip MPG on one gauge and instantaneous MPG on the other.
To daisy chain, hook up one gauge as you always do, then in the "second" connection spot, run a standard (not crossover) PC network cable from one gauge to the other. Before you try it, I'd recommend setting MODE to AUTO and RATE to SLOW on the car your trying this on. Some protocols are easier to daisy-chain than others, so expect limited results.
EDIT: Added hacks once I got the green flag
Ever long for a power cord for your SGII so you didn't have to go back out to your car with a pen to transcribe data. Turns out they are simple to make.
Edit: Had +/- inverted... fixed it... sorry guys, and thanks to 2002sl2no4 for finding the error
First lets name stuff. Call the button with the red circle around it the HOME key. Now look at the pins that you plug the plug into closest to the home key. Now call the copper wire closest to the home key PIN1 and the wire furthest from the home key (on that connector) PIN8. To power SGII outside of your car, hook a 9v battery too it. <Edit>
Negative (-) to PIN1 and Positive (+) to PIN8 </Edit>
Now if you want to record all your TODAY and PREVIOUS DAY trip data, you can simply pull it out of the car and throw it in your pack and power it with your DC power adapter.
Once you have it hooked to a 9v, you can put it in demo mode. To go into demo mode from the home (connecting) screen.
1) Press MORE>MORE>MORE
2) Press Lower Left button 5 times
3) Press HOME button
I can't think of any use for Demo Mode other than to demo it. One downside is that the miles and gallons the demo-car uses will be added to your totals. So it will pollute your tank, today and previous day trip data. Still kinda fun though. I'm trying to get all my friends interested, so this turns out to be a neat little trick.
Edit: Added a section below
I don't know about you, but I'm all for putting off till tomorrow, what should be done today. On that note, it's always a bit of a chore to sit down and write all my "CURRENT" mpg from trip to trip. "TANK" and "TODAY" I know will still be there when I get back to my car, but once SG goes to sleep, "CURRENT" is gone. So I figured out a way to make "CURRENT" stick (mpg at least), so you can dash into that meeting your late for, rest assured that you can log the data when you get back. Here's how.
1) Right before you power down, just go and peak at the "CURRENT" mpg.
2) Once that screen is up, power-down, and run like mad to catch your meeting.
3) When you return to the car, relaxed, pull out a pen and watch closely when you power up your car. For 1 second, your "CURRENT" mpg is still there.
4) Write it down quickly before it goes away and hypermile home.
I actually use this a lot since my garage is west facing. It gets well over 100 in there when I pull in, and the last thing I want to do is sit in that sauna and jot down figures. I usually catch it after dinner instead.