ASTM class 1, 2 or 3 (Class S or S-1) certified reference weights are used for what purpose?

• A. Calibrating an analytical balance or a pan balance.
• B. Calibrating a pH meter.
• C. Calibrating a thermometer.
• D. Calibrating an electrical conductivity meter.

Answer: (D)

Certified reference weights are used to ensure mass measurements are accurate. ASTM class 1, 2, or 3 (Class S or S-1) weights provide very tight tolerances and traceability to national standards, making them ideal for calibrating analytical balances and pan balances. By using these known masses, you can check and adjust a balance so that its readings match true masses across its operating range, and you can verify the balance remains stable and linear over time.

Calibrating an electrical conductivity meter isn’t done with weights, because EC meters measure how well a solution conducts electricity, which depends on solution composition, temperature, and the cell constant. They’re calibrated with standard solutions of known conductivity (and sometimes reference cells). Similarly, pH meters are calibrated with buffer solutions, and thermometers with fixed-point temperatures or ice-water references.