BQ32000: Clock Accuracy Calculation

Hi all

BQ32000 Datasheet says that pre-calibration accuracy is +/- 35 ppm under the test conditions VCC = 3.3 V, VBACK = 3 V, Oscillator on, TA = 25°C.

What is the meaning of this ppm value? How can we use this value for accuracy calculation?

for example, what is the accuracy of the Bq32000 after 1 week operation under  VCC = 3.3 V, VBACK = 3 V, Oscillator on, TA = 25°C ? 

BR, 

Cagdas