( وَالْوَزْنُ يَوْمَئِذٍ الْحَقُّ) (And the weighing that Day will be the truth): Meaning,  the precision on that Day will reach the point where they will be the truth themselves . Allah (swt) says:

 وَنَضَعُ الْمَوَازِينَ الْقِسْطَ لِيَوْمِ الْقِيَامَةِ فَلَا تُظْلَمُ نَفْسٌ شَيْئًا ۖ وَإِن كَانَ مِثْقَالَ حَبَّةٍ مِّنْ خَرْدَلٍ أَتَيْنَا بِهَا ۗ وَكَفَىٰ بِنَا حَاسِبِينَ 

(And We place the scales of justice for the Day of Resurrection, so no soul will be treated unjustly at all. And if there is [even] the weight of a mustard seed, We will bring it forth. And sufficient are We as accountant.) (Al-Anbiyaa: 47)

 And that is the epitome of justice; for the deeds to be weighed Allah (swt) says:

 فَمَن يَعْمَلْ مِثْقَالَ ذَرَّةٍ خَيْرًا يَرَهُ (7) وَمَن يَعْمَلْ مِثْقَالَ ذَرَّةٍ شَرًّا يَرَهُ (8)

((7) So whoever does an atom’s weight of good will see it, (8) And whoever does an atom’s weight of evil will see it.) (Az-Zalzala: 7-8)

(فَمَن ثَقُلَتْ مَوَازِينُهُ) (So those whose scales are heavy): The side where good deeds weigh heavier.

( فَأُولَٰئِكَ هُمُ الْمُفْلِحُونَ ) (it is they who will be the successful): (Success) is to win. The Arabic word used for (success) in this verse also means (to plough) and it is the stem word of farmer (Fallah), who ploughs the soil and therewith wins the crops.