A group of students is engaged in an activity in which they are measuring the…

Concept: When a practical/lab task is assessed, the indicators used should measure the student's experimental skill and procedure (correct instrument reading, correct instrument placement, correct handling technique) rather than whether the student's raw numeric result matches one fixed “textbook” figure. A real material sample (like ordinary tap water) can legitimately give a reading that differs from the idealised value, because the idealised value assumes a pure substance under standard conditions.

Application: Each of the four listed items is checked against this principle — does it probe the student's technique, or does it demand a single fixed numeric outcome?

• Attending to the thermometer's least count is a procedural-precision skill: it decides how finely a reading can be reported, so checking it is a legitimate assessment indicator.

• Keeping the thermometer clear of the beaker's walls is a procedural-technique skill: contact with the glass wall risks the bulb sensing the container rather than the liquid, so checking it is a legitimate assessment indicator.

• Insisting the reading come out as exactly 100°C is not a procedural-skill indicator: ordinary tap water carries dissolved minerals and other impurities, and the observed boiling point also shifts with local atmospheric pressure, so a real sample's reading is not guaranteed to land on the pure-water, standard-pressure figure. Judging a student's technique by whether they reproduce that fixed number confuses a property of the water sample with the student's competence.

• Using a stand to suspend the thermometer is a procedural-technique skill: it keeps the thermometer steady and correctly positioned in the liquid without touching the beaker, so checking it is a legitimate assessment indicator.

Cross-check: Three of the four items (least count, wall contact, stand use) are genuine measurement-technique behaviours that vary with how carefully a student performs the task — exactly what a performance indicator should probe. The remaining item ties the assessment to a single fixed numeric outcome that depends on the water sample and atmospheric conditions rather than on the student's technique, so it is the one indicator that is not suitable for this assessment.