The first, and most widely employed is the visual estimate.  This works well for most sample types.  The second type of quantification technique is the point count.  While more labor intensive it is somewhat less subjective than a visual estimate.  This can be important especially at low asbestos concentrations.  Both the accuracy and precision are improved with point counting.  And the more points analyzed the better the accuracy and precision of the method.
Limit of Detection or Reporting Limit: < 1%