Comparison Note — Systematic vs Random Errors — Notes

Feature	Systematic Error	Random Error
Definition	Consistent, reproducible offset from true value	Unpredictable, irregular fluctuations
Cause	Instrument calibration, personal bias, environment	Uncontrollable small variations
Direction	Always in same direction (always +ve or always −ve)	Both positive and negative randomly
Can be eliminated?	Yes — by recalibration or improved technique	Reduced but not eliminated by averaging
Effect on mean	Shifts mean away from true value	Mean converges toward true value with more readings
Example	Zero error in a vernier caliper	Fluctuating room temperature during timing
Remedied by	Calibration, correction factors	Taking multiple readings and averaging

Feature	Absolute Error	Relative Error	Percentage Error
Unit	Same as measured quantity	Dimensionless	Dimensionless (%)
Formula	$\Delta A$ = \|measured − true\|	$\Delta A$ /A	( $\Delta A$ /A) × 100
Use	Comparing same-unit measurements	Comparing accuracy across quantities	Expressing precision in percent