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`k = (Delta I) /I`

Enter a value for all fields

The **Weber Fraction** calculator computes the Weber Fraction ratio (k) of just-noticeable difference (ΔI) and the intensity of a stimulus (I).

**INSTRUCTIONS:** Enter the following:

- (
**ΔI**) Just noticeable Difference for Intensity - (
**I**) Base Level of Stimulus Intensity.

**Weber Fraction (k):** The calculator returns the ratio as a real number. However, this can be automatically converted to a percent via the pull-down menu

The **Weber Fraction** represents that the ratio of the just-noticeable difference (JND) and the intensity of a stimulus should remain about the same for a wide range of intensities. The formula for the Weber Fraction is:

k = ΔI / I

where:

- k = Weber Fraction
- ΔI = just noticeable difference of intensity of stimulus
- I = base level of stimulus intensity

For example, imagine that a weight is 100 kg. The JND for the weight is 5 kg, meaning that someone lifting the weight can tell that 105 kg is slightly heavier than 100 kg. The constant is determined by dividing the JND by the intensity level of the stimulus, so 5/100 = 0.05.

This value of k = 0.05 can be used for all other weights, as long as they are not on the extreme ends of the range. For example, doubling the weight from 100 kg to 200 kg should also anticipate doubling the JND, because the constant *k* remains the same: .05 * 200 = 10, so someone lifting the weight should be able to tell the difference between 210 kg and 200 kg.

The constant k should generally remain the same within a modality (light, sound, tactile pressure, etc.) but may be different across modalities. Humans should be able to reliably and consistently detect the change if it is proportionally equal to Weber's fraction.

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