Having a precise and a fast job scheduler model that resembles the real-machine job scheduling software behavior is extremely important in the field of job scheduling. The idea behind SLURM simulator is preserving the original code of the core SLURM functions while allowing for all the advantages of a simulator. Since 2011, SLURM simulator has passed through several iterations of improvements in different research centers. In this work, we present our latest improvements of SLURM simulator and perform the first-ever validation of the simulator on the real machine. In particular, we improved the simulator's performance for about 2.6 times, made the simulator deterministic across several same set-up runs, and improved the simulator's accuracy; its deviation from the real-machine is lowered from previous 12% to at most 1.7%. Finally, we illustrate with several use cases the value of the simulator for job scheduling researchers, SLURM-system administrators, and SLURM developers.