1. What is the difference between Accuracy and Readability?
It is common to confuse these two terms, but they represent different aspects of a balance’s performance:
- Readability: This is the smallest division that the balance can display. For example, if a balance shows a weight as 0.001g, its readability is 0.001g.
- Accuracy: This refers to the balance’s ability to show a value that matches the “true” mass of the object. A balance can be highly readable (showing many decimal places) but still inaccurate if it is not calibrated correctly.
2. How often should a weighing balance be calibrated?
The frequency of calibration depends on the environment and how critical the measurements are. Generally:
- Daily/Before Use: A “routine check” or “internal calibration” is recommended for high-precision analytical balances.
- Annually: A formal professional calibration by a certified technician is standard for most labs to maintain compliance with ISO or GLP standards.
- Whenever Moved: You should always recalibrate a balance if it is moved to a new location, as changes in local gravity and leveling can affect results.
3. What is the difference between “Zero” and “Tare”?
While both buttons reset the display to zero, they serve different purposes:
- Zero: Used to reset the balance to its absolute zero point when the pan is empty. It accounts for minor drifts or dust on the pan.
- Tare: Used when you place a container (like a beaker or weighing paper) on the pan. Pressing “Tare” ignores the weight of the container so that the display only shows the weight of the substance you add next.
4. Why does the weight reading on my balance keep drifting?
If the numbers on the screen won’t stay still, it is usually due to environmental factors:
- Air Currents: Even a slight breeze from an air conditioner or a person walking by can affect sensitive balances. This is why analytical balances have glass draft shields.
- Static Electricity: Static charges on plastic containers or the sample itself can pull the weighing pan up or down.
- Temperature: If a sample is much hotter or colder than the room, it creates air currents (convection) inside the weighing chamber, causing the reading to fluctuate.
5. What is “Minimum Weight” and why does it matter?
The “Minimum Weight” is the smallest amount of substance you can weigh on a balance while still maintaining a required level of accuracy. Because every balance has a small margin of error (uncertainty), weighing a very tiny sample (e.g., 2mg on a standard precision balance) might result in an error percentage that is unacceptably high for your experiment.
