Until I was able to remove all rulers with any inch markings on them, we had a problem like this in our Introductory Physics (PHYS 101) labs at the College of Charleston (SC); never mind confusion at the third grade level!
Here's a story that exemplifies that and that shows my motivation for outshouting the faculty on the philosophy of dual-unit rulers. My cork finally blew when some students measured and reported the length of a wooden block as 4.13 cm. I disputed that and asked them to show me how they got that result. They held a dual-unit ruler up to the wooden block and then showed me the "mark" that they read ... 4-13/16 inches. Yep, there's the four on the last big mark and just count up to 13 on the smaller marks, so that's 4.13 and since we're in physics it must be centimeters. Right? Argh!
I immediately broke all the dual-unit rulers and dual-unit meter sticks up into small pieces and threw them away. All that remained were metric-only meter sticks and the metric-only rulers that NIST had freely supplied me with. This caused quite a flap in the department (I could have been fired as lab manager) but I prevailed and on the next edition of lab manuals that I published all non-metric values disappeared as well. I did those in LaTeX and the old Word files disappeared, too. Since only a few of the faculty knew how to do LaTeX, and those were very senior people, nobody was able to undo my editing. Some were happy to see me retire a few years later.
Engineers will be third to last to metricate, physicists second to last, and astronomers dead last.
By the way, I use 500 mL bottles of water as "very close to half a kilogram" and 1 L bottles (or two 500 mL bottles) as "very close to 1 kg" as examples. Let folks heft them and compare the heft of other objects.
Jim Michael Payne wrote: ....
The interesting question to me was a picture of a green bean with an inch ruler marked in inches only with 3 graduations in between (for 1/4, 1/2 & 3/4 inches). The question was how many inches is the bean? To me it was 3-3/4 inches. The kid marked down 3.3. The teacher put down 3.5 (in red) crossed that out and put 4. Kids see calculators, they count the graduations and that becomes a decimal, hence 3.3. This is a good example of how and why the US does so poorly in math and science when compared to other nations.
....
Mike Payne
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