What is parallax error in chemistry?

In chemistry, a parallax error is a deceptive shift in an object's actual position due to personal perception. This type of error commonly occurs in a laboratory setting with the use of specialized measuring instruments called volumetric glassware.

A meniscus refers to the crescent-shaped upper surface of a liquid placed inside volumetric glassware, such as a pipette, buret or graduated cylinder. In reading the volume of the liquid, the observer should be at eye level with the meniscus. Otherwise, a parallax error occurs.

The reading is higher than the actual value when the observer's eye is below the meniscus. Conversely, a reading that is lower than the actual value results when the marking is viewed from an angle that is higher than the meniscus.