Agilent Technologies 93000 SOC Series Training Manual page 596

Pin Margin Algorithm
The search for the fail/pass transition point begins by testing at the
predefined limits of the search region and then if a pass/fail transition
is found it continues. By halving the distance between limits it
produces a new limit where it performs a test. If a transition is found it
reverses the direction again halving the distance to the limit before
performing another test. If no transition is detected it continues in the
same direction and halves the distance to the limit where it performs
another test. It continues in this manner until it reaches the resolution
of the parameter. The pass value closest to the transition is returned.
If the first pair of results, for the search limits, are pass/pass or fail/fail
then the search is discontinued and an error is reported.
This search method needs less steps than a linear search and so it is
faster. It also detects the transition value using the highest resolution.
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Agilent 93000 SOC Series User Training Part 1, October 2004