Issue in Consistency rotation of Vigor VS-2 servo

We are using Vigor VS-2 in Solar Heliostat project where we need very high accuracy of rotation.
I am using Servo.writeMicroseconds() command to rotate the servo.
We are using 600 to 2400 us for 0 to 180 degree of rotation. (600 us for 0 degree, 1500 us for 90 degree and 2400 us for 180 degree).
For 0 to 90 degree rotation, we are changing us from 600 to 1500. But the angle rotation is not accurate. Every time, we are getting +/- 5 degree of 90. Such we have found low consistency of Vigor VS-2 servo.
Also, when servo is energized, the shaft can move +/- 3 degree (approx).

How can we achieve the consistence rotation of servo vs-2?