frank10 12 Posted February 7, 2012 Share Posted February 7, 2012 We have two identical scales but a car came up 5.0 on one and 5.1 on the other... Could have caused a problem but it was not a derby fanatic's son so the mom grabbed a pocket knife and trimmed a sliver off the bottom. So I got to thinking... must be a way to test the scales. Just took a quick look online and determined that 5 oz = 141.747616 grams grams and the us mint sight tells me that a new us quarter is 5.670 grams ( http://www.usmint.gov/about_the_mint/?action=coin_specifications ) 25 quarters X 5.67 grams = 141.75 grams so we talking a difference of -0.002384 or 0.000084093125 oz (less than a thumb print?) Seems like a good way to pre-test the scales. Interesting point (to me, at least)... you could mix any combo of $6.25 worth of dimes, quarters and half dollars to do this since their weights are proportional to their values. Link to post Share on other sites
Scoutfish 16 Posted February 7, 2012 Share Posted February 7, 2012 I was told that either 10 dimes or 10 pennies equals one ounce of weight. But we found out that older pennies and dimes do not weigh exactly the same as newer ones...and that depending on how much wear and tear the coin had - bent egdes, nicks, wearing thin on one side - gave us a variety of different weights. The only place we have a real problem is when people try to sneak by the decimal point. Know what I mean? Our scale has number past the decimal point. Some of the dads will buy scales that read 3 or 4 places past the decimal point. So they think if thie car weighs 5.006 or 5.0019 on their scale, it will show up as 5.00 on ours. Of course, it doesn't work that weigh! The scales will automaatically read up and round up to the next digit. If your car weighs in at 5.009 on your scale...it will read 5.1 on ours. They complain that our scale is off, but I explain that even 5.0000000001 is still .0000000001 too heavy Link to post Share on other sites
packsaddle 753 Posted February 7, 2012 Share Posted February 7, 2012 For years, I provided the district weigh-in scale. I had the advantage of having a research-quality instrument. This led to occasional claims by persons with 'postal-quality' scales that mine was inaccurate. In each case I produced a set of NBS-certified standards to show that my instrument was 'dead-on'. This didn't satisfy them. They accused the standards as being wrong because their scale "matched what they got at the Post Office". Go figure. So even if you DO get access to actual standards, you're still going to have to defend yourself. Good luck. Link to post Share on other sites
AnnLaurelB 10 Posted February 7, 2012 Share Posted February 7, 2012 We have these little calibration weights... ...FAT lot of good it did us. It didn't matter that OUR scale was calibrated with "perfect" weights. What mattered was when the boys went to turn in for District last year, most of them were OVER on the host Pack's scale. We sat there for HOURS, trying to get our boys' cars under. It was horrible. You just can't predict one set of scales over another. Link to post Share on other sites
Tampa Turtle 1011 Posted February 7, 2012 Share Posted February 7, 2012 The scale is the scale is the scale. Our pack had only one "official" scale and yes you could show up and find you were at 5.1. One time it was all the graphite that pushed it over the rounding decimal. I have seen cars that were not painted on the bottom go over due to absorbing water through humidity. I would stick with one scale. To me half the fun is the tearing stuff off at the last minute to get under the weight limit. Many hand injuries helping the boys! Introducing other scales or weights will just add to disputes. Link to post Share on other sites
Eagledad 2784 Posted February 7, 2012 Share Posted February 7, 2012 >>You just can't predict one set of scales over another. Link to post Share on other sites
noname 10 Posted February 7, 2012 Share Posted February 7, 2012 dollar bill is 1 gram, a nickel is 5 grams. Try that out... Link to post Share on other sites
Eagle92 110 Posted February 7, 2012 Share Posted February 7, 2012 TT's problem is the one we encounter. It doesn't matter what scale you use whether USPS, or a NBS certified one, at home or at a pack meeting. If the car is over 5 onces on the scale used at the district PWD, it won't race until it is. And once it's weighed in, the Cubs won't touch it until race time. Link to post Share on other sites
SeattlePioneer 144 Posted February 7, 2012 Share Posted February 7, 2012 This is why I don't like overproduced Pinewood Derbies where parents are getting in the way of the boys having fun. Link to post Share on other sites
John-in-KC 311 Posted February 7, 2012 Share Posted February 7, 2012 Sounds like the District Activity Operations Committee should invest $60 for 5 oz of NIST approved field calibration weights, and then have them available for loan to Packs, and for the District PW event as well. Link to post Share on other sites
Eagle92 110 Posted February 7, 2012 Share Posted February 7, 2012 AH here's the interesting thing. Our district PWD is sponsored by a local club, and they own and do everything: track, scales, prizes, scheduling, etc. All the activities person does is get the info and pass it along. Link to post Share on other sites
Papadaddy 121 Posted February 7, 2012 Share Posted February 7, 2012 Consumer grade scales are probably only accurate +/- half an ounce, at best, and can be affected by temperature, humidity, etc. Can your scale be "tared" (zeroed)? If so, have someone take a car from last year, and take it to your local friendly lab and have it "certified" on a lab-quality scale. That is your "reference" car. Then put it on your scale and adjust the reading to the reference weight. Link to post Share on other sites
Twocubdad 665 Posted February 7, 2012 Share Posted February 7, 2012 The problem is with the rules, not the scale: "Cars will weigh 5 ounces or less weighed the day of the race on the scale provided by the pack. The pack scale is official." Of course you need to be fair and the scale need to be relatively accurate. BSA sells a brass 5oz. weight which we used to calibrate our scale. Tell the parents with the scale accurate to -12 decimal points to pound sand. Link to post Share on other sites
Eagledad 2784 Posted February 7, 2012 Share Posted February 7, 2012 >>Sounds like the District Activity Operations Committee should invest $60 for 5 oz of NIST approved field calibration weights, and then have them available for loan to Packs, and for the District PW event as well. Link to post Share on other sites
packsaddle 753 Posted February 7, 2012 Share Posted February 7, 2012 "Even the best precision instruments can get off, especially when they are moved or transported. Eventually you'll just have to pick a scale, make it official and declare the room a drama free environment." Not really, you don't just have to pick one. This is where the availability of a true standard can settle matters. If the scale is off, it is possible to determine that fact and by how much. Precision instruments can be transported but depending on the technology, there may be a special procedure. And they must be set up correctly. But once set up they should all perform the same. But again, the presence of a standard can show the truth of that. Or the problem if there is one. I was unaware that BSA sells such a standard. I applaud them for that...good job. My lab has 5 such instruments and all of them read exactly the standards accurately. They've been moved many times...one of them to all the pack and district derbies. Link to post Share on other sites
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