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
