Tafsir of Ar-Rahman 55:9

وَأَقِيمُوا الْوَزْنَ بِالْقِسْطِ (And observe the correct weight with fairness, ....55:9). The word قِسط qist literally means 'justice'. The meaning is obvious: 'And observe the weight with equity'.

وَلَا تُخْسِرُ‌وا الْمِيزَانَ (and do not make weighing deficient...55:9). The word خُسر khusr means 'to skimp or make deficient'. The opening part of verse [ 9] was the positive aspect of the injunction, and the concluding part is its negative aspect, in that it is unlawful to fall short of measure or weight. The two parts, positive and negative, put together the verse as a whole means 'Do not cheat in weights and measures, but rather observe justice and fairness'.