When you use weights for buying or selling things, you need to make sure the weight is clearly marked on the top or side. You should be able to easily read the numbers and letters that show how much the weight is.

If you use containers to measure liquids for buying or selling, you need to make sure the amount they can hold is clearly marked on the outside. Again, you should be able to easily read the numbers and letters.

For tools used to measure length when buying or selling, the markings need to be clear and easy to read.

If a weight or measure doesn't have these clear markings, it can't be officially checked and approved for use in buying and selling.

Remember, there might be some special rules about this in the law, so it's always good to check if there are any extra details you need to know.