Blank thermometer:

No numbers, no calibration marks, just a blank thermometer--essentially a thermoscope. A child can follow changes in temperature by watching the fluid rise and fall.

Everybody alive today was born into a world with calibrated thermometers--they're so obvious as to seem intuitive. Thermoscopes were invented long before Celsius and Fahrenheit got their names attached to them.

The thermoscope itself poses interesting questions. Why does the fluid inside change shape? How fast can you make it rise and fall? Does it always go down when things get colder? (A brilliant child might even ponder what it means to say "colder.")

Over time, children will get familiar with patterns. Ask a child if something is warmer (or colder) than something else. Is today warmer than yesterday?

At some point a child might think to put a mark on the thermoscope, maybe using a piece of tape, to compare one reading with another.

Eventually, of course, the thermoscope becomes more useful with its suit of numbers. Until a child needs the numbers, though, I suspect they just get in the way.


A blank balance:

My first chemistry set came with a super cheap plastic balance with tiny tin pans. A pointer indicated when the the two pans were level, but it couldn't measure anything, all it could do is compare.

The "all it can do" liability taught me more than a Ohaus Adventurer Pro AV64 Analytical Balance ever could--it was also about $1600 cheaper.

All any scale does is compare masses--a cheap balance just makes it more obvious what you're comparing. The fancy scale is comparing numbers based on a slab of platininum-iridium alloy sitting in Paris somewhere, slowly losing mass to entropy and time.

My cheap balance did not need a numerical reference. Either something had more (or less) mass than something else. It measured the relative pull of gravity of each item, nothing I would have understood when in kindergarten, and nothing I truly understand now.

Which is, of course, the point.

When we use unimaginably fine scales to measure (and the mass of 0.1 mg, the limit of the Ohaus scale, is truly unimaginable), we are dealing with an abstract precision that, at some level, detracts from our understanding of the world.

A child could learn more comparing a bowling ball and a duck using a large, simple balance than she appears to know when she reads 12.1213 grams on the Ohaus scale. She might sound smarter reading the fancy scale, especially in a culture that confounds the abstract with the real, and she might even impress a few administrators and BOE members along the way.

But she won't know a lick more science.

The photo is of the kilogram protoype in Paris.
The old thermometers is from the 1832 Edinburgh Encyclopaedia via  Engines of Our Ingenuity