Magnitude estimation: This term refers to estimating the intensity or strength of a stimulus. For example, trying to estimate how loud a sound is without any reference points.
Weber's Law: This law states that for humans to perceive a difference between two stimuli, the difference must be proportional to the magnitude of the original stimulus.
Just noticeable difference (JND): It refers to the smallest detectable change in intensity of a stimulus. For instance, noticing when someone turns up the volume on your favorite song just slightly.