Reference library91 entries

Author: Tommy C. Moran

Practical explanations, worked examples, and reference notes for reporting numbers correctly.

Oct 2026

Significant Figures in Excel: How to Round to a Given Number of Sig Figs

Excel has no built-in significant-figures function, but you can round to n sig figs with a formula using ROUND, LOG10, and ABS; understanding Excel's…

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Oct 2026

Measurement Uncertainty

Why Do Some Textbooks Use the Full Scale Division for Uncertainty Instead of Half? A Comparison of Conventions

Textbooks disagree on whether reading uncertainty is half or one full scale division because they assume different interpolation models, conservatism levels, and digital count…

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Oct 2026

Significant Figures

Why Did My Teacher Mark This Wrong? The 7 Most Common Sig Fig Mistakes in Chemistry

A chemistry teacher marks significant-figure answers wrong when the reported digits overstate or understate measurement precision. Here are the 7 most common sig fig…

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Oct 2026

Significant Figures

Why Does My Calculator Give a Different Sig Fig Answer Than My Teacher?

Calculators do not track significant figures; they compute at full precision. Your teacher applies measurement-based sig fig rules and a rounding convention, which can…

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Oct 2026

Accuracy vs Precision

Trueness vs Accuracy: The VIM Definition and Why It Matters in Calibration

Understand the critical distinction between trueness and accuracy according to the VIM, and how these concepts govern precision measurement and rounding standards.

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Oct 2026

Exact Numbers

Why Is a Mole Exact? The Difference Between a Count and a Measurement in Chemistry

The mole is exact because the SI defines it by an exact fixed value of the Avogadro constant; however, most laboratory amounts are obtained…

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Oct 2026

Chemistry

Significant Figures in Molarity and Dilution Calculations: Precision and Rounding

In molarity and dilution calculations, report the result with the least number of significant figures among multiplication/division inputs; for added volumes, first apply the…

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Oct 2026

Significant Figures

Significant Figures in Engineering Drawings: How to Read and Apply Tolerance Rounding

Engineering drawings use significant figures and decimal places to encode precision and tolerance. Learn the standards, rounding rules, worked examples, and pitfalls for reading…

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Oct 2026

Significant Figures

How to Round a Number in Scientific Notation to a Given Number of Significant Figures

Round the coefficient to the required number of significant figures, apply the correct tie convention, and renormalize if the coefficient reaches 10.

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Sep 2026

Chemistry

Percent Error in Chemistry: AP, IB, and High School Grading Conventions

Percent error in chemistry is |experimental − accepted| ÷ |accepted| × 100%, but AP, IB, and high-school grading differ on sign, sig figs, and…

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