Screen grab from Vernier caliper applet

Vernier calipers and the venerable screw micrometer allow us to measure small objects with a resolution high enough to see random variation – I use air gun pellets (0.177” BB shot) with a micrometer reading to 0.01mm and the resulting dot plot of the diameter of 30 pellets shows a pleasing normal cluster but with clear gaps between the readings showing how the instrumental resolution affects the results.

Screen grab from micrometer applet

The screen grabs are taken from a couple of excellent Java applets by Ron Blond that demonstrate dynamically how these instruments work. Projecting these and inviting the students to read the scales speeds up the process of learning to read the instruments considerably.

There will be some means and standard deviations here soon

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