Error Types

Theory of Error

1.0 DEFINITIONS

1.1 ERROR

This word is used to denote the difference between a measured value and a "true" value. It is also used to indicate the degree of- uncertainty by expressing it in quantities as standard deviation, probable error, etc...

1.2 DISCREPANCY

This is the difference between two measured values such as between two students or between the student's reading and the published value.

2.0 CLASSIFICATION OF ERRORS

2.1 SYSTEMATIC ERRORS

2.1.1 ERRORS OF CALIBRATION OF INSTRUMENTS

2.1.2 PERSONAL ERRORS

An example of this would be parallax errors caused by the observer always holding his head to one side of an indicating needle.

2.1.3 EXPERIMENTAL CONDITIONS

If an instrument is calibrated under one set of conditions but is used under another set of conditions, the readings will be wrong.

2.1.4 IMPERFECT TECHNIQUE

An example would be where a flow reading is being made by timing the flow of liquid into a graduated cylinder and a small amount splashes out.

2.2 RANDOM ERRORS

2.2.1 ERRORS OF JUDGEMENT

For example, when a needle is between two mark's then it will be a judgment call as to whether the reading should be .7 or .8, for example.

2.2.2 ERRORS CAUSED BY FLUCTUATING CONDITIONS

An example would be in taking amperage readings when the line voltage is fluctuating.

2.2.3 SMALL DISTURBANCES

For example, trying to weigh something when nearby machinery is causing vibrations. The Injection Blow Molding machine is very sensitive to temperature changes. If the door is opened and closed quickly or the forced air furnace comes on, it will have a small effect on the process.

2.2.4 DEFINITION

For example, the lack of good definition of a boundary will make it difficult to get consistent readings. An irregular edge of a table will make it difficult to measure the width of the table.

2.3 ILLEGITIMATE ERRORS

Most...