What should be the sample rate of ADIS16495 to accurate measurement of delta angle and velocity


I am using ADIS16495 . I want to measure the position of sensor (means at which angle it present) and i want to measure accurate velocity of sensor.

i am using it at it's internal frequency and DEC_RATE set to 2, now sample rate is 1416.66 sps rate. when i am using this sample i am getting wrong calculated values and when i set to  1 sps sample rate then i am getting right calculated values.

Please reply what am i doing wrong.