Need to understand the purpose of epsilon value in the PathInterestFactory class

Neo4j Graph Platform Graph Algorithms/Graph Data Science
1

Can someone please help me to understand what is the Significance of Epsilon value in the following class : org.neo4j.graphalgo.impl.util.PathInterestFactory
this class has following method :
public static PathInterest allShortest( double epsilon ) { return new PriorityBasedTolerancePathInterest( epsilon ); }

What is the value we should give for epsilon. I am using neo4j 2.3.8