This paper presents the results of 16 years of monitoring stellar orbits around the massive black hole at the center of the Milky Way using high-resolution near-infrared techniques. The study refines previous analyses by improving the coordinate system definition and investigating systematic error contributions. The long time baseline and excellent astrometric accuracy of adaptive optics data allow the determination of orbits for 28 stars, including the star S2, which has completed a full revolution since the monitoring began. The main findings include: 1. **Orbit Fit**: All stellar orbits are well-fit by a single point mass potential, with astrometric uncertainties reduced to approximately 6 times better than in previous studies. 2. **Central Object Mass**: The mass of the central object is estimated to be $(4.31 \pm 0.06)_{\text{stat}} \pm 0.36)_{\text{rho}} \times 10^6 M_{\odot}$, with a fractional statistical error of 1.5%. 3. **Distance to the Galactic Center**: The best estimate for the distance to the Galactic Center is $R_0 = 8.33 \pm 0.35$ kpc, with systematic errors being the dominant source of uncertainty. 4. **Mass Scaling**: The mass scales with distance as $(3.95 \pm 0.06) \times 10^6 (R_0/8 \text{ kpc})^{2.19} M_{\odot}$. 5. **Orbital Angular Momenta**: The orientations of orbital angular momenta for stars in the central arcsecond are random. 6. **Star Types**: Six stars are identified as late-type stars, and six as early-type stars, confirming their membership in the clockwise rotating disk system. 7. **Extended Dark Mass**: The mass enclosed between the pericenter and apocenter of S2 is constrained to be less than $0.066 \times 10^6 M_{\odot}$ at the 99% confidence level, significantly larger than other theoretical and observational estimates. The paper also discusses the data acquisition, analysis methods, and the construction of a combined coordinate system to improve the accuracy of the astrometric measurements.This paper presents the results of 16 years of monitoring stellar orbits around the massive black hole at the center of the Milky Way using high-resolution near-infrared techniques. The study refines previous analyses by improving the coordinate system definition and investigating systematic error contributions. The long time baseline and excellent astrometric accuracy of adaptive optics data allow the determination of orbits for 28 stars, including the star S2, which has completed a full revolution since the monitoring began. The main findings include: 1. **Orbit Fit**: All stellar orbits are well-fit by a single point mass potential, with astrometric uncertainties reduced to approximately 6 times better than in previous studies. 2. **Central Object Mass**: The mass of the central object is estimated to be $(4.31 \pm 0.06)_{\text{stat}} \pm 0.36)_{\text{rho}} \times 10^6 M_{\odot}$, with a fractional statistical error of 1.5%. 3. **Distance to the Galactic Center**: The best estimate for the distance to the Galactic Center is $R_0 = 8.33 \pm 0.35$ kpc, with systematic errors being the dominant source of uncertainty. 4. **Mass Scaling**: The mass scales with distance as $(3.95 \pm 0.06) \times 10^6 (R_0/8 \text{ kpc})^{2.19} M_{\odot}$. 5. **Orbital Angular Momenta**: The orientations of orbital angular momenta for stars in the central arcsecond are random. 6. **Star Types**: Six stars are identified as late-type stars, and six as early-type stars, confirming their membership in the clockwise rotating disk system. 7. **Extended Dark Mass**: The mass enclosed between the pericenter and apocenter of S2 is constrained to be less than $0.066 \times 10^6 M_{\odot}$ at the 99% confidence level, significantly larger than other theoretical and observational estimates. The paper also discusses the data acquisition, analysis methods, and the construction of a combined coordinate system to improve the accuracy of the astrometric measurements.