Scales. Need advice

[Roger Nuffer]

I do the weigh in for our pack. The digital scale I use is only accurate to 1/8 ounce. If a car weighs just under 5 1/8 ounces it'll show as 5 oz. So I need something better.

What are your packs using to weigh in the cars?

[gpraceman]

Our pack uses the Ohaus CS200, http://www.scaleman.com/ohaus/cs200.html. It is a pretty good scale overall and measures down to 0.01 ounces.

Here's a few scale buying tips from my GrandPrix Race Central website:

Digital Scale Buying Tips

In trying to purchase a new digital scale or in evaluating your current one, these are some of the things you should consider.

• Weight Capacity - Since scales come in different weight capacities, you should get the lowest possible capacity that will measure 5 ounces (141.75 g). A scale with a higher weight capacity will also have a higher measurement error, since a scale's accuracy is generally 1% - 2% of the weight capacity.
• Number of Digits Displayed - I recommend getting a scale that will display at least to 0.01 ounces, since hundredths of an ounce can have a measurable effect on finish times.
• Scale Calibration - A good scale will have a calibration feature that will allow you to adjust the displayed measurement to match a known standard weight. If the scale can't be calibrated and is off when measuring a standard weight, you may have problems with parents that have used a more accurate scale. Some scales come with the calibration weight, some don't. If not, you can purchase one.
• Accuracy - Accuracy is a measure of how close the scale can measure a known weight to its "true" weight (taking the average of repeated measurements). To be accurate, a scale should measure a known weight to within 0.1% or better of its value. A 5 ounce weight should weigh in within +/-0.005 ounces so the measurement would be accurate to the hundredth of an ounce that is shown on the scale's display.
• Precision - Precision is actually more important than accuracy and is a measure of how closely repeated measurements are from each other. Since variation is inevitable, the scale will not always hit the bull's eye every time, but the spread of the measurements should be very small. I recommend that you get a scale that has a precision of at least 0.0035 ounces (0.1 grams).

On the calibration weight, it is nice if you can find a scale that calibrates to a certified 5 ounce weight, instead of a 200g weight. It is easier to show parents that the scale is working properly if you can put the 5 ounce weight back on the scale and it still reads 5.00 ounces. MaxV has a scale like this (http://www.maximum-velocity.com/special ... tm#measure) and some of the other PWD suppliers may have as well.

[Stan Pope]

Our pack uses the Ohaus CS200
...
On the calibration weight, it is nice if you can find a scale that calibrates to a certified 5 ounce weight, instead of a 200g weight. It is easier to show parents that the scale is working properly if you can put the 5 ounce weight back on the scale and it still reads 5.00 ounces.

Excellent point, Randy! In addition to the CS200's certified 200.0g calibration weight, I supply our district races with a couple of 5.000 oz "confirmation" weight for "quick checks" before sending someone off to trim their car's weight down.

[Stephen's Dad]

I'll second the Ohaus CS200 although our Pack also owns a CS2000. We use both but the 200 is closer to perfect.

For our own shop I also have a new Ohaus Scout Pro 400 I picked up on eBay for less than $100. I opted for this because it included some extra items like an AC wall adapter/transformer.

We have the 200 gm weight but we also have two of the 5 oz weights for all of the reasons already cited.

I just checked eBay & there are six Ohaus CS200s with "Buy it Now" listings for $48.88. This is a great deal.

http://search.ebay.com/search/search.dl ... category0=

[Stan Pope]

We have the 200 gm weight but we also have two of the 5 oz weights for all of the reasons already cited.

The CS200 is a good accuracy for the application... 0.1 not tight enough; 0.001 takes too long to stabilize and too sensitive to environment.

Scaleman says that the CS200 has some quality problems, and one of my two scales now has very dim LCD's in the top half of the display. Suspect cold solder joint, but I couldn't find anything suspicious around the LCD connections. But, otherwise, I really like those scales.

Watch out for the BSA catalog's 5.0 ounce "weight standards" ... they are only good to 0.04 oz last time I read the catalog. They will "prove" the CS2000 in the BSA catalog, but not the CS200!

[Stephen's Dad]

Stan Wrote:

Watch out for the BSA catalog's 5.0 ounce "weight standards" ... they are only good to 0.04 oz last time I read the catalog. They will "prove" the CS2000 in the BSA catalog, but not the CS200!

Yes...This is the reason we have 2 of everything. After we purchased a CS200 we discovered how far off the BSA 5 oz weight was! Now our "Official" weight has about 15 pieces of tape stuck to it to bring if from 4.95 oz right up to 5.0 oz. The same weight did weigh 5.0 oz on the CS2000 that is in the catalog. It still weighs 5.0 oz on all of the scales. But the CS2000 is too "coarse" to detect the small difference.

[Stan Pope]

Suspected that you knew that already, but that there may be a few readers who had not yet noticed the issue... those in the buying mood. Thanks for sharing your experience with the CS2000.

[Stan Pope]

When I was trying to decide on a scale, I took typical car features into Michael Lastufka's simulation program to estimate the effect of various scale accuracies... 0.1, 0.01, and 0.001 oz.

I found that car weight difference that would still show as equal on a 0.1 oz scale would allow too much difference at the finish line... in excess of a quarter inch, IIRC. 0.01 and 0.001 weight differences were both barely perceptible at the finish line. Actual experience with a 0.001 scale showed it to be too "fussy" with ambients (air motion, table motion, ...) to be effective in the rapid-fire inspection environment.

I don't know that the CS200 was the best choice (I've been happy with it), but I'm convinced that the 0.01 accuracy was the best choice.

[gpraceman]

I'm going to give the scale offered by MaxV try. I just ordered it the other night. I like not having to keep up with two different standard weights, one for calibration (200.0 g) and one to put parents minds (and mine) at ease (5.00 oz). I'll let y'all know how it goes with that scale.

I agree with you Stan that the "standard" weight carried by BSA just isn't accurate enough to be used with a scale accurate to 0.01 oz. I do notice that the scale being sold by BSA is only accurate to 0.1 oz, so that weight will work fine with that scale. That looks like the scale that I use for weighing postage. It is good for that purpose, but definitely not one that I would use for check-in.

I would caution everyone on purchasing a 5 ounce weight (or any other calibaration weight) that doesn't gaurantee that it is certified to be +/- 0.001 ounces or less. I have seen many on eBay that make no claims as to the accuracy of the weight, so buyer BEWARE.

[gpraceman]

This seemed like a good time to review and update the information on scales on my GrandPrix Race Central website.

One of these was an added recommendation to check for overload protection on a digital scale. Unfortunately, I have seen racers go up to a scale and see just how hard they can press down on it . It is good if a scale has some type of protection from having the maximum weight limit exceeded. Anyways, I feel that a check-in scale should never be left unattended.

[gpraceman]

I'm going to give the scale offered by MaxV try. I just ordered it the other night. I like not having to keep up with two different standard weights, one for calibration (200.0 g) and one to put parents minds (and mine) at ease (5.00 oz). I'll let y'all know how it goes with that scale.

Well, unfortunately, I have nothing good to report on this scale. I tried to calibrate the scale with the 5.00 +/- 0.00021 oz weight, but when I put the weight back on the scale, it would read 4.98 oz. Scales USA sent me another scale and it had the same issue. It turns out that this scale has an accuracy of only +/- 0.03 oz, so that 5 oz "calibration weight" could display from 4.97 to 5.03 oz. I would have a hard time trying to explain that to a parent if we were trying to hold everyone to a 5.00 oz limit. In reality, how much of an impact would this measurement error have? Probably not much, but to me, if a scale displays to 0.01 oz, then a 5.00 +/- 0.00021 oz weight should display it as 5.00, not 4.97 and definitely not 5.03.

The other things that I didn't like on this scale were the buttons and the operation of the scale. The buttons do not give any tactile sense that the button was pushed. They have to be pushed harder than expected to work. For calibration and changing from grams to ounces you have to push the On button for so many seconds but nothing happens until the button is released. I was rather expecting that after holding the button for the required time the scale would start the calibration procedure or do the change from grams to ounces. I could have lived with these things, but not the accuracy issue.

With our old pack we used an Ohaus CS200 and didn't have these problems. The BSA 5.00 +/- 0.004 oz weight displayed as 5.00 oz. I don't have access to our current pack's Ohaus CS200 scale so I don't know how well that one works as I am not involved in check-in. However, I am being told by one scale vendor not to buy an Ohaus due to poor quality.

So, I am going to try some other scale and see if I fare any better. I contacted Precision Weighing Balances (http://www.scaleman.com) and tried asking a couple of questions but the guy was very rude. He continued talking to someone while I was trying to ask my questions, just tried to refer me to their website info, and then said "this isn't rocket science" and suggested I go somewhere else. Lovely customer service. Needless to say I will.

[pinewood nut]

Hello to all, and a big thanks to everyone here! (found this site just before our pack race and the little I learned then helped us to take 1st in Wolf class) I've been lurking for a while, trying to soak in all the good info and figured I'd finally get to some posting. Has anyone tried thisscale from Harbor Freight?

I went down to our local store the other day and they didn't have any in-stock (though it seems to be available on their web site). I was just looking for something at home to measure our car in-progress (districts in a few weeks, building a new car) I'd love to go with one of the pricier scales mentioned above, but the Wife has about had it with PWD purchases and I don't think I can convince her on a 60+ dollar scale

[PW Grasshopper]

I do the weigh in for our pack. The digital scale I use is only accurate to 1/8 ounce. If a car weighs just under 5 1/8 ounces it'll show as 5 oz. So I need something better.

What are your packs using to weigh in the cars?

Roger, does your district race use a more accurate scale or does it round to the nearest 1/8 once?

[Roger Nuffer]

I have no idea what the district does. Wish I did. I suggested in the pack committee meeting that we use the district racing rules and got blank stares. My pack does not seem to be much involved with the district. We were recently moved from one district to another and this has caused some issues.

Our pack is small so they are rather relaxed. We even have open time after the cubs race for anyone who brought an old car or built a new car. I'd like to tighten things up a bit but oh well.

I bought a Jennings CJ-600 with an AC adapter, 500 gram tare and separately purchased a 5 oz tare.

The CJ-600 is dead on. After I calibrated the scale with the 500 gram tare it hit 5.00 oz every time. I got my own car (The official pace car) to read exactly 5.00 oz. I checked last years pace car and it was 5.06 oz. What a difference an accurate scale can make.

Tonight is the derby race. I'm ready. 5 cars have been built at my house over the weekend. Next year I'll host workshops.

I'll let you all know how the CJ-600 performed under pressure as well as how the event went. It will most likely be chaotic and slightly disorganized.

Roger

[Roger Nuffer]

Hello to all, and a big thanks to everyone here! (found this site just before our pack race and the little I learned then helped us to take 1st in Wolf class) I've been lurking for a while, trying to soak in all the good info and figured I'd finally get to some posting. Has anyone tried thisscale from Harbor Freight?

I went down to our local store the other day and they didn't have any in-stock (though it seems to be available on their web site). I was just looking for something at home to measure our car in-progress (districts in a few weeks, building a new car) I'd love to go with one of the pricier scales mentioned above, but the Wife has about had it with PWD purchases and I don't think I can convince her on a 60+ dollar scale

The instructions show the the scale can be callibrated with a 200g or 500 g weight. This should improve the scale accuracey.

This looks like a pocket scale. Could be difficult to read and or ballance the cars on the scale.

Then again I'm new to all this.

Roger

PS. I'm always leary of HF product quality.