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wdb · 06-23-2013, 07:22 AM

Precision != accuracy.

I think it's important to point out that a UG or SG display value is only as good as the data it gets. Both devices are reading data from the car's computer, which is reading data from sensors spread throughout the car. The abililty of the sensors to accurately translate physical phenomena to voltage, and the quality and -- very importantly -- the resolution of the analog-to-digital conversion of those volts, combine to become the source of the data you see on the gauge.

So, for example, If you have a speed sensor + A/D converter combination that is capable of producing figures with an accuracy of +/- 1MPH, the fact that your Ultragauge is capable of displaying MPH in tenths is literally useless. Not only that, you should expect to see the numbers go up or down by 1 or 2 MPH.

But wait, you say. Some cars have digital speedometers, and I don't see them jumping around! That's because the manufacturers have beaten you to the punch, and they've thrown some averaging gizmoid in there to 'smooth' the output so that it doesn't jangle the poor driver's nerves. I can't say for sure but I doubt UG/SG does much in the way of smoothing - they probably just repeat the raw numbers they're fed.

then factor in the SG/UG doing calculations of its own, such as MPG. Now you're adding even more uncertainty and variability to the output.

So I'll repeat something I've said before. SG/UG, used as relative measures, are extremely useful as tools to gauge how your driving style affects gas mileage. If you start comparing the numbers they produce to the numbers you see from other instruments and expecting everything to line up all honky dory, you will drive yourself needlessly crazy.

Calibrate them by all means, but don't expect perfection. Get them close, then leave the calibration settings alone and start comparing driving style to the numbers you see on the UG/SG. That's where the real value lies.

06-23-2013, 07:22 AM	#16 (permalink)
wdb lurker's apprentice Join Date: May 2008 Location: the Perimeter Posts: 942 PlainJane - '12 Toyota Tacoma Base 4WD Access Cab 90 day: 20.98 mpg (US) Thanks: 504 Thanked 226 Times in 173 Posts	Precision != accuracy. I think it's important to point out that a UG or SG display value is only as good as the data it gets. Both devices are reading data from the car's computer, which is reading data from sensors spread throughout the car. The abililty of the sensors to accurately translate physical phenomena to voltage, and the quality and -- very importantly -- the resolution of the analog-to-digital conversion of those volts, combine to become the source of the data you see on the gauge. So, for example, If you have a speed sensor + A/D converter combination that is capable of producing figures with an accuracy of +/- 1MPH, the fact that your Ultragauge is capable of displaying MPH in tenths is literally useless. Not only that, you should expect to see the numbers go up or down by 1 or 2 MPH. But wait, you say. Some cars have digital speedometers, and I don't see them jumping around! That's because the manufacturers have beaten you to the punch, and they've thrown some averaging gizmoid in there to 'smooth' the output so that it doesn't jangle the poor driver's nerves. I can't say for sure but I doubt UG/SG does much in the way of smoothing - they probably just repeat the raw numbers they're fed. then factor in the SG/UG doing calculations of its own, such as MPG. Now you're adding even more uncertainty and variability to the output. So I'll repeat something I've said before. SG/UG, used as relative measures, are extremely useful as tools to gauge how your driving style affects gas mileage. If you start comparing the numbers they produce to the numbers you see from other instruments and expecting everything to line up all honky dory, you will drive yourself needlessly crazy. Calibrate them by all means, but don't expect perfection. Get them close, then leave the calibration settings alone and start comparing driving style to the numbers you see on the UG/SG. That's where the real value lies.