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Snellen chart

a device for testing visual acuity, consisting of printed letters ranging in size from very small to very large. The observer reads the letters at a given distance. Also called Snellen test. [Herman Snellen (1834–1908), Dutch ophthalmologist]

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Psychology term of the day

September 8th 2024

drift

drift

n.

1. a reduction in variation in genetic traits that can occur when sampling from continually smaller groups, such that some traits ultimately become excluded from possibility.

2. a reduction in the reliability of technical instruments orin the accuracy of observers over time. See instrument drift; observer drift.