[rules-users] Monitoring sensor parameter change

Hello, I am using Drools with Guvnor and Drools Fusion. I have application that read data from sensors and after each read insert event to StatefulKnowledgeSession. I have some basic rules that works. Now I need to detect when one of sensor parameter change by some value between reads from given sensor, e. g. Lets say I want to detect when power rise by more then 2: 4 sensor reads (4 events inserted to session) 1. power=0.9 2. power=1 3. power =4 --> rule should detect that fact (4-1=3 ; 3>2) 4. power = 2 I do not now how to get access to previous reads in rule to do subtraction (4-1=3). Any advice appreciated. Thanks, Bartek