Thursday, June 30, 2011

Poor quality: The Science Museum's keyring thermometer

I have a small keyring bought from The Science Museum that has a compass and a thermometer on it. I wondered how good the thermometer was so I stuck it in a glass of iced water:

Hmm. It appears to be showing that the water/ice mixture is at -6C.
So then I stuck it in my freezer which is at -18C.

Hmm. It appears to be showing that the freezer is at -25C. So I stuck it in the fridge with a separate digital thermometer.

Hmm. Fridge appears to be at 7C and the thermometer is showing 1C. So, a final test at basement temperature (18C).

Hmm. Looks like about 13C.

So, here's the pattern:
Iced water0-66
Which roughly means that the thermometer reads 6C lower than the actual temperature. I'm guessing that the scale and the actual thermometer glass were badly stuck together. 6C difference is only a couple of millimeters.


WoJ said...

You get the 6 deg difference based on the reading of the digital thermometer.
Is that one calibrated correctly (does it for instance show 0°C for melting ice?)

John Graham-Cumming said...

I used the digital thermometer for two of the measures, the fridge's own thermometer for the freezer and the temperature of iced water from memory.

benc said...

This post reminds me of a visit to the observatory at greenwich a decade ago where they displayed a wall of poorly synchronised clocks that the geek in me was horrified to see.