ScanGaugeII Calibration Worksheet

Discussion in 'ScanGauge' started by Dan, Aug 25, 2007.

  1. Dan

    Dan KiloTanked in post 153451

    ScanGaugeII Calibration Worksheet

    I've had some requests to go into a bit more detail on the calibration worksheet. Here's the basic premise on it, posted in the Tips and Tricks thread...

    Confusing... yeah I know. I'm not too gifted at turning math into English. Hopefully by restating the points there will be sufficient convergence.

    So the spreadsheet basically takes a known good estimate of your mileage and compares it to Scangauge's view of your mileage. Works good if your known good is a car maker's fuel consumption display (like on the Prius), but not so good when the "known good" is a gas receipt. Problem is, it's hard to fill your tank to the same level every time. So when you under-fill on one fill-up and over-fill on the next, the calibrations vary wildly. So what is needed is an averaging mechanism (that I left out of the first draft). I'll correct it this weekend, so we might be able to fix it.

    Let's take what's out there now.

    The SGII comes with a calibration method that adjusts the actual gallons used and the measured gallons used. This is covered in the manual, so I won't dwell on it. My problem with this is that it doesn't offer enough granularity. Both speed calibrations and gallon calibrations effect the measured MPG. So what the spreadsheet does is predict the effect of both of these calibrations on a given tank.

    Time for an example:
    Lets say at your next fillup your ODO says you made 386.4 miles on your tank.
    Now lets say SG reported your tank distance as 384.1.

    SG underreported distance by 0.5988 %

    Let say that at this fillup you put in 17.513 gallons
    And SG reported 17.3 gallons consumed.

    SG over reported gallons by 1.0565 %

    So now at fillup, you change 17.3 to 17.5. Done right?

    Lets see how that lines up.

    SG(now) = 384.1 / 17.5 = 21.82386
    Actual = 386.4 / 17.513 = 22.06361

    So even after the calibration, SG is under reporting MPG by 1.10%

    Now try with the spreadsheet.
    Put zero next to MiAdj, RQMi, GalAdj
    Put 386.4 next to MiFCD
    Put 384.1 next to MiSG
    Put 22.06361 next to mpgFCD
    Put 21.82386 next to mpgSG

    Now you will see that RQGal has changed to -1.09. The spreadsheet is suggesting you adjust gallons down by 1.09%. Close as we can get on SGII is 1.1%. So test it by putting -1.10% next to GalAdj.

    Now you'll see that the mpgTST field went to 22.07. This is what SG would have reported WITH the calibration. So the spreadsheet got you a lot closer (22.07) than the normal calibration methods (21.82).

    Now since distance is borderline we could test what would happen if we did a 1% adjustment on distance. So since SG underreported distance by 0.59% we could round up to 1%.

    Put 1% next RQMi
    Put 1% next to MiAdj

    The spreadsheet now suggest dialing gallons down by 0.10%. So try putting -0.10% next to GalAdj, and you will see the prediction changed from 22.07 to 22.06.

    So those are two calibrations you could try in this hypothetical
    {Speed = 0%; Gallon = -1.1% } = 22.07 mpg
    {Speed = 1%; Gallon = -0.1% } = 22.06 mpg

    both of which are trying to zero in on your tank numbers of 22.06361

    I'll be making some revisions for averaging soon... So stay tuned.

  2. xcel

    xcel PZEV, there's nothing like it :) Staff Member

    Hi Dan:

    ___You can also change the speedo/distance on the fly. If you are over by 5 miles at the 250 mile point, you can back off the distance by 1% and then let that offset build in. At the 500 mile point, it may be dead on which means you are a bit below actual now.

    ___A 1% addition/subtraction can be manipulated on the fly but that does not mean it will be more accurate over a tank in terms of actual mpg. Lead foot the first 250 miles and make the speed/distance adjustment and hypermile the rest and your actual will be even further off :(

    ___Anyway, just thought I would add this opportunity to approach actual in a shortened time frame rather then wait to run through a whole tank if you are short on time. I know someone who is ;)

    ___Good Luck

  3. Dan

    Dan KiloTanked in post 153451

    Updated to Version 1.1 on 8/30/2007 for better documentation and history.

  4. 2way

    2way Electromagnetic Wave [:-h


    Isn't E5 supposed to =E4*(1-E3) ?

    Your SG measured Miles seems to be in reverse.... If I am @ +1%, then the SG reports +1% more than it measures. Using your E5=E4*(1+E3), your spreadsheet will say that the SG measured higher miles... when it actually measured a shorter distance.
    Last edited: Feb 20, 2008
  5. Dan

    Dan KiloTanked in post 153451

    Your right! The relation is inverted, on cell E5 for both sheets. Changing to E4*(1-E3) doesn't fix it, but changing to E4/(1+E3) does. This isn't readily apperrent until you put in a huge delta. If you try 50% on a reported distance of 300, your measured should be 200. This is because 200 * (1 + 50%) = 200*1.5 = 300.

    Sorry for the confusion guys.

    Thanks for the catch 2-way.

  6. 2way

    2way Electromagnetic Wave [:-h

    :thumbs_up: NP, you're welcome. It just didn't make sense to me. Thanks for your work on this.

    But, I guess I should go back to math class and bone up on %'s ;)
  7. Dan

    Dan KiloTanked in post 153451

    Added Version 1.2 on 4/16/2008 to correct error in E5 (noted in help thread).

    sorry for the delay.

  8. n3rdyguy

    n3rdyguy Member

    Is it possible to make a version for us that uses litres/100km?
  9. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    Hello, N3rdyGuy and welcome to CleanMPG!!
  10. Dan

    Dan KiloTanked in post 153451

    n3rdyguy... Welcome as well. I suppose I could rev a version 1.3. PM me if I forget or if it falls off my list. The math should be strait forward, I just need too sit down and work it out.

  11. BrianWillan

    BrianWillan New Member

    Just convert your liters/100km to km/liter and then use the spreadsheet as is. The spreadsheet is essentially unit independent. Meaning that it wouldn't really know the difference if you entered a km for miles or liters for gallons, as long as the units are consistent.


    Brian Willan
    Oshawa, Ontario
  12. jdhog

    jdhog Hyper Smiler

    This looks like useful info. I'm coming up to my first fill while having a SG so I'll be needing to read this again soon to help me calibrate it. Thanks!
  13. morfes

    morfes Member

    I have a question about how am I use this utility.

    I go to the gas station and I fill up
    I write down to a paper the data we need to fill the spreadsheet.
    Then I need to go at my home to fill it so I should do some km. At the gas station I reset the data as you suggest at the spreadsheet without adjust anything.
    I go home and the spreadsheet calculate for example that I need to adjust the fuel at the sg 4%.When should I adjust it? Because this moment the sg has already done some distance from the gas station to my home....
  14. Dan

    Dan KiloTanked in post 153451

    Well I was carrying it on my cell phone so that solved your immediate problem.

    Plus the spreadsheet will simply zero in on a calibration setting over multiple tanks. You can just follow one tank behind the spreadsheet if you like. Won't effect the math since I factor out whatever calibration you have set.

    So plug in TankA get CalibA. When you fill TankB, set you calibration to CalibA, then go home and fill in your tank to get CalibB. When you fill TankC, set your calibration to CalibB.... One tank behind.

  15. morfes

    morfes Member

    Thank you very much for your answer , but I have a question more. Every time I fill up , I will use a new tank at the step 2? I mean tha I don't erase the previous data and should I write the new one so the spreadsheet calculate all of the fill ups?
  16. Dan

    Dan KiloTanked in post 153451

    Yes, the top bold line of step 2 is the accumulated total. Add each tank into a blank row in step 2. This will sum all the tanks together to help get a very accurate picture of the required calibrations.

  17. morfes

    morfes Member

    Thank you again! I test it and I will post the results!
  18. Showbizk

    Showbizk Well-Known Member

    The only problem I've had with this is by the time I get home after filling and make the spreadsheet entries to calibrate, I lose about 4 miles of data on the tank, since changing the calibration zeroes out other entries...
  19. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    Any time within the first gallon, you can change the offsets on the fly. Just go to fillup and adjust it, but don't hit save. Sure, the first 4 miles might be off by 1%, but that's not much.
  20. morfes

    morfes Member

    But If I do that and not hit save , it doesn't save the offset...

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