Measuring and uncertainty
Good readings
- Resolution: the smallest change an instrument shows. A burette reads to 0.05 cm³; a measuring cylinder to 1 cm³ or worse.
- Read volumes at eye level from the bottom of the meniscus.
- Repeat, spot anomalies, leave them out, take a mean.
uncertainty ≈ ± half the range of the repeats
Errors and the words for data
- Random errors scatter readings; repeats and means reduce them.
- Systematic errors shift every reading the same way, such as a balance that is not zeroed (a zero error).
- Precise: repeats close together. Accurate: close to the true value. Repeatable: same person, same method agrees. Reproducible: others get the same.
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