A balance can display a small number without measuring that amount with the accuracy an experiment requires. Readability describes the display; judging a small peptide sample mass requires information about measurement performance and the intended use.
Read the last digit for what it is
METTLER TOLEDO describes readability as the smallest increment shown on a balance display. Its analytical-balance guidance separately discusses repeatability, environmental conditions and minimum weight, making clear that these are different properties.METTLER TOLEDO — Analytical Balances (opens in a new tab)
For an original example, a display increment of 0.1 mg means that successive displayed values can differ by 0.1 mg. It does not establish that a displayed 1.0 mg is correct within 0.1 mg or suitable for a particular study.
Adding digits to a spreadsheet after transcription cannot increase the information supplied by the measurement. A value entered as 1.0000 mg should not imply finer resolution than the balance record supports.
The relevant quantity is the sample’s net mass, not the much larger gross mass of the container and sample together. A heavy vial does not turn a small material increment into a large net sample.
Relate absolute uncertainty to sample size
The manufacturer’s guidance defines relative uncertainty by comparing absolute weighing uncertainty with the load and explains that minimum weight depends on working conditions and the required accuracy. A single universal minimum cannot be inferred from the instrument name.METTLER TOLEDO — Analytical Balances (opens in a new tab)
| Net mass | Assumed uncertainty | Relative value |
|---|---|---|
| 1 mg | 0.1 mg | 10% |
| 10 mg | 0.1 mg | 1% |
| 100 mg | 0.1 mg | 0.1% |
The assumed 0.1 mg is supplied solely for this calculation. It is not derived from readability, and the table is not a performance specification for any balance.
The arithmetic explains why a modest absolute uncertainty can become consequential for a small sample. Whether the resulting percentage is acceptable depends on the measurement’s role in the study.
Look for evidence that applies to the actual weighing
A device specification, a calibration record and an individual sample record answer different questions. The device description states nominal capabilities; the other records connect performance and use to a particular instrument and context.
Check that a quoted uncertainty or minimum weight belongs to the balance and conditions used. A value copied from a different instrument’s certificate cannot establish the performance of this measurement.
If the notebook records only a mass and no instrument link, identify the missing information rather than assuming that the laboratory’s most precise balance was used.
State the limit without inventing a correction
When reviewing a small-mass record, preserve the reported value, units and available instrument evidence. If the required performance cannot be established, describe that limitation directly.
Do not round a questionable measurement towards the intended target or substitute the label claim for the observed mass. These changes would conceal the uncertainty rather than address it.
A suitable summary explains what was displayed, what uncertainty evidence exists and whether that evidence addresses the study’s required net mass. It leaves any unresolved performance question visible for the responsible laboratory.
Sources and further detail
- METTLER TOLEDO — Analytical Balances (opens in a new tab)
Manufacturer guidance checked for readability, relative uncertainty and condition-dependent minimum weight. No product recommendation or universal minimum mass is inferred.
Sources checked 20 September 2026. Numerical examples are hypothetical unless attributed to a study. Measurement explanations are not laboratory protocols or product handling limits. This article has not undergone independent scientific peer review.