(Give full measure, and cause no loss.) meaning, `when you give to people, give them full measure, and do not cause loss to them by giving them short measure, while taking full measure when you are the ones who are taking. Give as you take, and take as you give.'
وَزِنُواْ بِالْقِسْطَاسِ الْمُسْتَقِيمِ
(And weigh with the true and straight balance.) The balance is the scales.
وَلاَ تَبْخَسُواْ النَّاسَ أَشْيَاءَهُمْ
(And defraud not people by reducing their things,) means, do not shortchange them.
Some scholars have held the word Quistas as a Roman word, which means justice, while others have taken it as an Arabic word, derived from Qist, which is also used for justice. It means to make use of the scale and other measuring tools in a straight and correct manner, where there is no possibility of weighing less.
Tazkirul Quran
Maulana Wahiduddin KhanOn ayahs 175–183
The area to the south and east of the Dead Sea now appears to be deserted. But, from 2300 to 1900 B.C., it was a very flourishing area, inhabited by the people of Lot. In spite of his continuous preaching, they did not reform themselves. On the contrary, they were out to kill him. Then they were destroyed by a severe earthquake. One part of this area is buried in the Dead Sea, while the other part exists only in the shape of ruins. This event happened four thousand years ago. Lot’s wife could not rise above the traditions of her community. In spite of being the prophet’s wife, she remained loyal to her community’s religion. As a result, when God’s punishment was administered, she was killed along with the common unbelievers.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.