Saturday, November 26, 2011

Measuring with Anchor

One of my recent projects involves an electronic weight scale, and I've been using various items for rough calibration. I thought I was onto a "Great Milk Conspiracy" when I discovered that my 1 liter bottles of milk only contained 950 cc. But upon further investigation, it turns out that my trusty Anchor Hocking Company measuring cup (bought from a Walmart, in Hawaii I think) is not accurate! After lots of head scratching, I finally weighed various levels of water on a commercial, precision scale. You can see the data here:

Bottom line, there seems to be an offset to the printed scale - for kitchen purposes let's call it 10 cc. For scientific purposes, I would say don't use this - get an accurate graduated cylinder or beaker instead. Well, at least I have solved the milk mystery. Next, I'm going to solve the rice conspiracy (5 out of 5 bags of 1Kg bags weigh EXACTLY 990 grams)...

1 comment:

Tuttle said...

Two potential flaws in your experimental design is the failure to account for purity and temperature. The theoretical mass value you use is actually only true of pure, distilled water at 4 degrees Celcius. Your observed slope matches pure distilled water at 60 degrees Celcius perfectly. I'll grant you that's somewhat warmer than you were probably using, but the impurities in tap water could make a substantial difference in density.