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Guru Nanak sang in Ragas since he had knowledge of all these as can be seen from metre and measure of his Shabadas. While recording, the Raag, Ghar and Rahao were entered bu Guru Nanak and later this became a tradition which all Gurus followed. Guru Arjan did minor modifications to ensure that the system is throughout the same. He added Mahala and where the ragas were not mentioned he evaluated the Shabdas, its history and thereafter assigned the raaga, Ghar and Rahao. The compilation was a great job done by Guru Nanak with the assistance of Bhai Gurdas. They were holy men and did their work with utmost sincerity and in the spirit of the writers. Event the writings of other saints and Bhagtas were evaluated by Guru Arjan and assigned to the Ragas accordingly.