# Weighing Accuracy in Simple Words

> What 'accurate weighing' really means, why a scale can be wrong even when it looks precise, and what makes the result better or worse.

- Page: https://ocs.com.ua/en/wiki/weighing-accuracy/
- Publisher: OS-Technology Ukraine

"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)](https://ocs.com.ua/en/wiki/what-is-scale-division/). 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](https://ocs.com.ua/en/wiki/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.