Estimation of service interval
 
 Mean 103 km
 Standard deviation σ 103 km
 R(t)1 -
 R(t)2 -
 
  Interval 1 Interval 2
 z - value - -
 service interval t 103 km 103 km
 a1 = R(t2) / R(t1) -  
Timing belt replacement: http://en.wikipedia.org/wiki/Timing_belt
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