To create the "Trade Against the Gap" system by Stephane Reverre in MetaStock 6.52 or higher, select System Tester from the Tools menu, click New and enter the following code:

Name: Trade Against the Gap

Enter long:
     GapLong := 3;
     GapShort := 3;
     Gap := 100*(CLOSE-Ref(CLOSE,-1))/Ref(CLOSE,-1);

     Gap <= -GapLong

Close long:
     GapLong := 3;
     GapShort := 3;
     Gap := 100*(CLOSE-Ref(CLOSE,-1))/Ref(CLOSE,-1);

     BarsSince(Gap <= -GapLong) = 1

Enter short:
     GapLong := 3;
     GapShort := 3;
     Gap := 100*(CLOSE-Ref(CLOSE,-1))/Ref(CLOSE,-1);

     Gap >= GapShort

Close short:
     GapLong := 3;
     GapShort := 3;
     Gap := 100*(CLOSE-Ref(CLOSE,-1))/Ref(CLOSE,-1);

     BarsSince(Gap >= GapShort) = 2

Click OK, then click Options, on the Testing page under Trade Price set both the Entry and Exit Price to Close and set both Delays to 0.