Tuning forks used in psychology

Tuning forks are used in research of the auditory senses. By having one of the tuning forks as a "base" tone, or 0, you can label the other tuning forks as +1, +2, +3, etc. and use these numbers to study the limits of auditory learning between subjects. Researchers will use one toning fork to see which subjects can hear different tones and whether or not other subjects can hear those same tones. This will allow researchers to see what the common tones are for subjects to be able to hear, which will then allow doctors to discriminate between people with hearing disorders. If 99.99% of people can hear a certain tone that one person cannot, it is likely that this one person has a hearing disorder.