Weighing Accuracy in Simple Words

“This scale is accurate” is something everyone says, but what does it actually mean? Let’s make it clear.

The short version

Accuracy is how close the scale’s number is to the real weight.

If a product really weighs 500 g and the scale shows 500 g, great. If it shows 503 g, the scale is off by 3 g. That 3 g is the error. The smaller the error, the more accurate the scale.

Think of darts

Imagine throwing darts at a target:

• Accurate: darts land close to the bullseye.
• Repeatable (precise): darts land close to each other, but maybe far from the bullseye.

A scale can be repeatable but not accurate. For example, it always shows 3 g too much. The numbers look stable and trustworthy, but they are all wrong in the same way. This is why scales need to be checked against a known weight from time to time.

Accuracy is not the number of digits

A scale showing 150.23 g is not automatically more accurate than one showing 150.2 g. The extra digit is just finer display, which is explained in the article about resolution (d). Accuracy depends on the quality of the whole scale, not on how many digits it shows.

What makes weighing less accurate?

Think of weighing as a very sensitive measurement. Anything that pushes, shakes or heats the scale can spoil it:

• Vibration. Motors, nearby machines, a person walking by.
• Air drafts. A fan or an open door can push on a light product.
• Temperature changes. The sensor inside the scale reacts slightly to heat and cold.
• Dirt and sticking product. Dust, glue or leftovers on the belt add extra weight.
• Uneven or unstable base. A scale that is not level or stands on a shaky floor gives shaky results.
• Moving products. On a conveyor the product is only on the scale for a fraction of a second, so it is harder than weighing something standing still.
• Worn or damaged parts. The load cell can drift or be damaged by overload.

How to keep it accurate

You don’t need to be an expert. A few habits help a lot:

1. Install the scale properly. Level, stable, away from strong vibration and drafts.
2. Keep it clean. Wipe off dirt and product residue.
3. Don’t overload it. Never put more than the maximum weight on it, and avoid hits and drops.
4. Let it warm up for a few minutes after switching on.
5. Check it regularly with a known test weight. If the number is wrong, adjust (calibrate) the scale.

How much error is OK?

It depends on what you are weighing. Ask yourself: how many grams of difference can I accept in one pack?

• If you pack 500 g bags and can accept ±5 g, a scale with a 1 g error is plenty good.
• If you weigh medicine doses of 2 g, you need a much finer and more accurate scale.

Choose the scale based on your tolerance, not on the biggest possible number of digits.