S1.1 Experimental techniques

Move from hazard to control

Identify the specific hazard, who or what could be harmed, and how exposure could occur. Then choose a control that removes the hazard or reduces probability or severity—for example shielding and distance for ionizing radiation, insulation for hot equipment, or containment for pollutants.

Protect self, others and the environment

Check the investigator, nearby people, organisms, equipment and surroundings. After applying controls, state any residual risk and whether the investigation should proceed, be redesigned or not be performed.

Frame an ethical choice

Compare benefits and harms for the affected people. For a medical isotope, balance possible treatment benefit against side effects and the consequence of not treating; do not present a medical choice as risk-free.

Discuss rather than list

A discussion needs more than one perspective or consequence and a reasoned comparison. For environmental questions, consider extraction, use, disposal and long-term effects.

Common trap

Do not write a vague claim such as “it is dangerous.” Name the mechanism and the consequence, then connect it to the decision.

Choose and prepare the instrument

Match range and resolution to the expected value and required precision. Check calibration, zero, units and viewing geometry before measuring mass, time, length, volume, temperature, force, current, potential difference, angle, sound intensity or light intensity.

Read the value

Record enough digits to reflect the instrument’s resolution and include the unit. For a corrected reading, apply the zero offset with the correct sign; a displayed value is not automatically the true value.

Worked example — signed zero correction

A caliper shows $20.60\,\mathrm{mm}$ around a sphere but reads $-0.30\,\mathrm{mm}$ when closed. True diameter $=20.60-(-0.30)=20.90\,\mathrm{mm}$. Subtract the zero reading algebraically; do not guess the correction direction.

Improve reliability

Repeat measurements, average them, and measure at different positions or orientations when geometry permits. This reveals random variation and reduces its effect on the mean.

Common trap

Do not increase precision by writing extra decimal places that the instrument cannot resolve, and do not correct a zero error in the wrong direction.