Electric meter readings - tenths or hundredths?

I have been trying to check the accuracy of my electricity meter, and have discovered that the last two red numbers following the main meter reading appears to record tenths, not hundredths. If this is normal, why not just have one red number? At he moment, every time it goes up by ten, the main meter reading increases by one.
Is everyone's meter like that, or do I have a dodgy meter?
Ross
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Meters vary. At work we have three meters that I read to track utilities. One is multiplied by 60, another 200, still another by 640. Is there a factor noted on the meter itself?
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Thanks for replying Edwin. Yes there is a factor which says 166 two/thirds revs/kWh. But I can't work this anywhere into the equation. I suppose this refers to the wheel going round?
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Ross wrote:

I have never had a meter that ha any red numbers, but I can't imagine a kiloWatt-hour meter that measured closer than 0.1 kiloWatt-hour.
How are you checking the accuracy of the meter reading? If you are checking it against stated watt usage of an appliance, you will likely have a problem, e.g., a 100 watt light bulb. I've never tested one that used exactly 100 watts. You probably need an expensive VOM to read actual amps and voltage to get accuracy.
You can check the watt usage for very short periods of time if you want to count revolutions of the meter disk. On the meter face you will see a K(subH) = (some number) somewhere. This is a constant for that particular meter. Watts (not kilowatts) equals ((number of disk revolutions) x 3600 x K(subh))/ seconds.
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By the way this is a Brit meter so that explain it somehow. I'm encouraged by your remark that you can't imaging a kWh meter measuring closer than 0.1. I thought about testing it by turning on my 750 watt microwave for say, 10 minutes and calculating the desired usage. But there are other appilances in use, fridge, freezer etc that it wouldn't be accurate.
I couldn't find a K(subH) that you mentioned. Below the meter reading there is 240v - S 200.31 - 166 2/3 revs/kWh - 1PH 2W - Class 2 0 - Floton. Beneath 240v, there is 20 80A and 50Hz. It is a Sangamo Western meter and is the property of South Eastern Electricity Board. Most of this is double dutch to me George, but it may mean something to you?
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Ross wrote:

Well, that it explains it, British! :) the 50Hz is a clue it isn't U.S. since all of our stuff is 60 cycles/second. I haven't looked at British meters so don't know how to interpret the 166 2/3 revs/kWh, but I would bet it means that the disk turns 166 2/3 revolutions for each kWh. Solving the equation that I have you for K(Subh) using 166 2/3 revolutions results in a K(Subh) of 6.00 which is well within the range of the meters I have seen.
If you do test something, don't use anything that has a motor, and certainly not a microwave. (btw was the microwave 750 watts output or input? If input that is really a weak microwave since output could be as low as 600 watts. Straight resistance is best, for example, turn everything else off and turn on lights with a total wattage of 1000 watts. You won't be accurate but you should be within a reasonable error.
If I were you, I would call up the electric company, ask for a technician, and ask him/her what everything meant and how to check the accuracy of the meter (they'll probably do it if you have had excessively high bills). You might get nowhere, but you also might get all the info you want.
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Thanks George, good advice - I'll do that
Ross
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It is a simple Kwh meter. The numbers you provide indicate which meter it is. The best thing you can do is call your supplier and ask for some one to come out and explain it to you. The 80a means that the meter will handle 80 amps. Hz is self explanatory. I have not a clue what the 20 is.
Here in the US meters read left to right. That gives you a number. Some meters are direct read, they actually read correctly. On large users I have seen multipliers of 1000. I have seen multipliers on homes of 5-10. Each meter can and may be set by the utility for a specific purpose.
The odds that you will be able to "check" your meter are astrominical. I have been working on meters for 20 years. You need specific calibrated equipment. Utilities where I live are allowed by Arizona law to be within 3%. I know a lot of the meter guys and they established plus or minus 0.5%. I have seen 3 residential meters out of calibration in 30 years. One was low and the customer was bitching. He really bitched when they fixed the problem. Commercial demand meters in the old days were subject to some whims and could wander out of calibration. I know of one that has been wrong for 10 years and the customer knows it the utility knows it and they leave it alone. It took me 6 months and well over 100K of equipment to prove the meter was wrong. The utility just made an adjustment for that month and lowered the kwh charge for future bills. End result was the same.
If you think your bill is to high look carefully on your side. Something running more than it should or a new load. Chances are it is on your side of the meter not their side.
It might be possible for something in the meter to be awry, odds are against ya..
Everything above is referenced from the USA. Should be close enough for where you are.
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Thanks for taking the time to reply in such detailed manner. All makes very interesting reading, particularly the complications involved in checking a meter's accuracy. My reason for originally doubting my meter's accuracy was that quite a few units get clocked up during the night. I've turned off all appliances that were previously on standby or on a clock (microwave, video etc), but I have a fridge/freezer AND a freezer. The freezer frequently freezes up quickly so I now think that it is inefficient and is probably the reason. Both are half empty so I plan to move all contents to the fridge/freezer, turn the freezer permanently off and see if electric usage drops.
Thanks again for such an interesting insight.
Ross
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