Ed, Not to sound pissy but I would still chose a used Ohaus Triple Beam for $45. I have far to many years working in electronics to trust digital measurements. Most of those years managing the calibration schedule for test equipment.
Cub ----- Original Message ----- From: "Ed Reeder" <[EMAIL PROTECTED]> To: "clubmaker online" <[EMAIL PROTECTED]> Sent: Tuesday, June 15, 2004 6:17 PM Subject: ShopTalk: Initial Electronic Scale Evaluation > I purchased a "My Weigh" i500 scale and wanted to give an > initial evaluation. So far it has been wonderful. > > Today was 98 degrees where I live and when the unit was delivered > I set it up inside, 78 degrees, and started measuring. I > measured the 500g calibration weight that came with it and > got 499.7g. I then measured 5 heads from Wishon that had > their weights listed. The weight and each head were measured > four times as the unit cooled from 98 degrees to 78 degrees. > The cooling period was about 30 minutes. The unit was turned > off and on multiple times during the tests. > > The calibration weight was 499.7g each time. The heads measured > the same weights 16 of the 20 (5 x 4) times. Twice I got a +0.1g > difference and twice I got a -0.1g difference. This while the > unit was cooling from 98 to 78 degrees. The scale "stabilized" > its readings very quickly, much quicker than my old 1000g GS scale. > > I calibrated the scale to 500g and performed a series of measurements > over a 30 minute time period. Each of the six times I measured > the calibration weight I got 500.0g. Three of the five heads > measured exactly what Wishon said (e.g., 251.8g). The two that > were off were .4g and .5g too much (to jump ahead, I believe > the i500's values more than what was marked on the heads). > > I measured the heads multiple times and got EXACTLY the same > results each time. I then put an 8.1g weight on the scale and > measured the heads. Each was increased by 8.1 grams. I then > "tare'd" the scale with the 8.1g weight on it. I then measured > each head again. Four were exact and two were 0.1g light. > > I tried a 153.3g weight in the same way as the 8.1g weight. Here > two values were increased by 153.3g and three were increased by > an additional 0.1g. I "tare'd" the scale and weighed the heads. > Four of the five were exact and one was 0.1g heavy. > > I then weighed and "tare'd" weights of 0.5g, 0.7g, 1.9g, 7.5g, > 38.1g, 251.8g, and 500g. Each time the appropriate weight was > replaced the scale read 0.0g! I did this multiple times with > the same results. > > Once calibrated and cool, the only time the scale was even off 0.1g > was when I was weighing two items and expected the total of the two > weights to add up. However, when weighing two or more items you > aren't accounting for cumulative rounding errors (e.g., 5.54g + > 3.54g = 9.08 [rounds to 9.1] while you are expecting 5.5 + 3.5 = 9.0) > > Later in the evening, when cooler, I turned the scale on and > got 499.9g. I did this repeatedly with the same results. The > heads were each likewise 0.1g light. > > Bottom line. It appears the scale is VERY repeatable and accurate. > The only issue seems to be a slight sensitivity to temperature. > (The scale does have compensation for temperature changes). However, > you can simply check for a possible anomaly with the calibration > weight and easily perform a calibration if desired. > > The scale and a 500g calibration weight were $77.76 including shipping. > > http://www.precision-balances.com/myweigh/i500.html > > /Ed > >
