Enrichment · Passion Projects · Lab science

Your thermometer is a little off.
Here is by how much.

Check the thermometer in an ice bath and at a second known temperature. The calculator works out its offset and gain and corrects every reading you give it.

CalibrateWhat you get

The calibration calculator

The worked example is made up: a lab probe reading 0.4 in ice and 99.1 in boiling water at sea level. Nothing you type leaves this browser.

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What you get

Enrichment · Passion ProjectsFree

What you finish with
A one-point offset or a two-point correction line, a list of corrected readings, and checks on the reference points. It prints as a summary and downloads as a spreadsheet.
Who it is for
Chemistry, biology and physics students, teachers maintaining lab probes, science fair students, and cooks checking a thermometer.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard, in °C or °F. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Passion Projects space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Make a well-stirred ice bath of crushed ice and a little water; read the thermometer.
  2. Read it at a second known temperature, ideally against a reference thermometer.
  3. Type both pairs.
  4. Paste readings to correct.
  5. Print the correction and tape it to the probe’s case.

Calibrate

How the correction works

A straight line through two known points.

The worked example: probe BGain1.0132(100 − 0) ÷ (99.1 − 0.4)Offset-0.41 °C0 − gain × 0.4Reading 37.237.28 °C1.0132 × 37.2 -0.41Reading 64.064.44 °CcorrectedThe worked example: probe BGain1.0132(100 − 0) ÷ (99.1 − 0.4)Offset-0.41 °C0 − gain × 0.4Reading 37.237.28 °C1.0132 × 37.2 -0.41Reading 64.064.44 °Ccorrected
Two known temperatures fix a straight line from what the probe says to what is true. One point can only shift readings; two points also correct their spacing.

One point or two

A thermometer can be off in two ways: shifted (it reads 0.4 too high everywhere) and stretched (its degrees are slightly too big or small). One reference point measures the shift. Two points far apart measure both, and give a line: true = gain × reading + offset. Between the points the correction is reliable; outside them it is an extrapolation.

Good reference points

A slush of crushed ice and water, stirred, sits at 0 °C. Boiling water is 100 °C only at standard sea-level pressure; at a school 300 m up it boils near 99 °C, so look up or measure the local boiling point, or use a reference thermometer with a calibration certificate. Keep the two points at least 10 °C apart.

Sources

  1. National Institute of Standards and Technology. Special Publication 250-23, Liquid-in-Glass Thermometer Calibration Service, and the ice point as a reference (nist.gov).
  2. National Institute of Standards and Technology. NIST Chemistry WebBook: water, boiling point and vapour pressure (webbook.nist.gov).
  3. U.S. Food and Drug Administration. Food Code: calibrating food thermometers in ice water (fda.gov).
  4. OpenStax. Chemistry 2e (2019), section 10.3, Phase transitions: boiling point and pressure (openstax.org).

The worked example is made up. Take care with boiling water. Your readings stay in this browser. Support: team@caveatacademic.com.