It may be obvious if a stick is crooked or it may not. It is most obvious if it is set alongside a straight stick. In the physical world there are standard measurements (straight sticks) such as the standard lengths on the wall of the Royal Observatory, Greenwich, with which potentially crooked sticks (shopkeepers' measures?) can be compared.
These straight sticks exist in the mental world too. Variants in English spelling can be referred to the Oxford English Dictionary.
In ethics involving morality and right behaviour, for some people the equivalent of the wall of the Royal Observatory might be Moses' Stone Tablets of the Law. The equivalent of the O.E.D. might be the Bible.
Or the Koran. Or the Vedas. Or the Avesta. Or Das Kapital.
There lies the problem. If there is more than one stick claiming to be straight and they are not identical, the adherents of each will view each of the others as crooked. The result can only be trouble. Today, now, look at the world. You will see the kind of trouble it leads to.
This is a universally applicable straight stick:
Avoid Bad. Cultivate Good. Purify your mind.
Bad is doing to other beings what you not like them to do to you.
Good is being helpful, kind and considerate.
Purify your mind is understood in the sense of purifying water; where all adulterants are removed, leaving pure water.
NEW PROJECT: CHOOSING TO CAN'T