O-Level Physics Error & Uncertainty Masterclass

TL;DR
SEAB’s 2026 O-Level Physics syllabus (6091) expects you to quote readings to the correct precision, propagate uncertainties, and discuss limitations for ACE marks (Section 4, Practical Assessment, SEAB 2026 syllabus).
Use absolute + percentage uncertainties, keep significant figures consistent with instrument resolution, and tie every ACE statement to how an error changes your conclusion.
Pre-build a commentary template: state result ± uncertainty, compare with accepted value, identify dominant error, propose a realistic fix.

1 | Precision rules every candidate must memorise

• Instrument dictates precision: Quote metre-rule readings to 0.1 cm, vernier caliper to 0.01 cm, micrometer to 0.001 cm, and stopwatches to 0.1 s unless otherwise stated (Section 4, SEAB 2026 syllabus).\
• Write what you record: Raw tables must show units in headings (Length / cm) and use consistent decimal places aligned with the measuring tool.\
• Calculated quantities follow the weakest link: When you compute density, resistance, or refractive index, round to the same number of significant figures as the least precise raw input.

✅ Quick check: before leaving a table, scan the decimal places column by column. Any mix like 12.0 vs 12.00 means a lost mark in PDO.

2 | Uncertainty toolkit (with sample numbers)