Using measurement norms

Record body data in SI units with correct significant figures and read it against a baseline to judge homeostasis.

Builds on (2 levels back)inferred · med confidence

A number needs a unit: '37' is meaningless until you say 37 degrees Celsius; reading body data depends on always attaching the unit.
Comparing a value to a reference: Judging homeostasis means comparing a reading to a baseline, which requires the idea of measuring against a known value.

Prerequisites are inferred: pending teacher review.

Re-learn the skill with worked practice and clear examples.

Record body data in SI units, and keep only the significant figures the tool can actually report. Significant figures are the digits a measuring tool can be trusted to give, so a reading of 37.0 degrees Celsius claims more precision than 37.

Step 1: Define significant figures

Significant figures are the digits in a measurement that the tool genuinely measured and can be trusted. A scale that reads to the tenth of a kilogram gives a value like 62.4 kilograms (three significant figures). Writing more digits than the tool can read would be making up precision.

Step 2: Keep the trailing zero when it is real

On a digital thermometer that reads to a tenth of a degree, 37.0 degrees Celsius and 37 are not the same claim. The 37.0 says the tool checked the tenths place and found zero, so the trailing zero is a real, significant digit you should write.

Step 3: Stay consistent across a data set

Record every reading to the same precision the tool allows so values can be compared and averaged fairly.

Practice

A digital thermometer that reads to the nearest tenth of a degree shows a patient's temperature as 37.0 degrees Celsius. How many significant figures does that reading have?

Reviewed

A.One
B.Two
C.Three
D.Four

Show the worked solution ▾

Answer: C. Three

Step 1: Identify the measured digits: The tool measured the 3, the 7, and the tenths place shown as 0 (a real reading, not a placeholder).
Step 2: Count them: That is three digits the tool actually measured: 3, 7, and 0.

Why it's right: The digits 3, 7, and the measured trailing 0 are all significant, giving three significant figures.

Why the others miss:

A: One ignores two of the digits the tool actually measured.
B: Two drops the measured trailing zero, which is a real significant digit here.
D: Four counts a digit that was never measured; the reading only has three.

Aligned to HBS Launch: significant figures · reading level ~grade 9

Where you'd see this

A lab data table that mixes 37 and 37.0 in the same column hides which readings were taken to the tenth: consistent sig figs fix that.

Careers that use this

Phlebotomist: Logs sample volumes and patient vitals to the precision the equipment allows so results are not over- or under-stated.

Video library

Watch: Using measurement norms

Unit Conversion & Significant Figures: Crash Course Chemistry #2

CrashCourse · ~11 min

Guided notes

Fill these in as you work through the lesson.

Big idea: Body measurements are recorded in standard SI units with the right number of significant figures, then compared to a baseline to see whether the body is holding homeostasis.

Key terms: write the meaning

SI units (the worldwide standard system scientists record in):
Significant figures (the digits in a measurement that the tool can actually trust):
Homeostasis (the body holding an internal value steady):
Baseline (the normal reference value you compare a reading to):

The rule

Record body data in standard units, keep only the digits your tool can trust, called , and compare the reading to the to judge whether the body is keeping its internal conditions steady.

Check yourself

Give the SI unit you would record for body temperature and for mass.
If a digital thermometer reads 37.0, why is the trailing zero worth writing instead of just 37?
What does it tell you about homeostasis when a reading drifts far from the baseline?

Work one example

A thermometer reads 38.5 and the baseline body temperature is 37.0. State the SI unit you must attach to each number, give each value to one decimal place, find how far the reading is from baseline, and say what that suggests about homeostasis.