FileMaker Pro Custom Functions

//note: dunning's site is truncating this Function //Last argument should be "listLength" not "list" //PolygonAreaHelper ( xlist ; ylist ; prevDep ; prevDMD ; i ; listLength ) //dependency: must be called from main function, PolygonArea Let ([ i = i+1 ; Lat = MiddleValues ( ylist ; i ; 1 ) - MiddleValues ( ylist ; i-1 ; 1 ) ; Dep = MiddleValues ( xlist ; i ; 1 ) - MiddleValues ( xlist ; i-1 ; 1 ) ; DMD = Dep + prevDep + prevDMD; DArea = Lat * DMD ]; DArea + If ( i < listLength ; PolygonAreaHelper ( xlist ; ylist ; Dep ; DMD ; i ; listLength ) ; Let ([ //innerLet Lat = MiddleValues ( ylist ; 1 ; 1 ) - MiddleValues ( ylist ; listLength ; 1 ) ; Dep = MiddleValues ( xlist ; 1 ; 1 ) - MiddleValues ( xlist ; listLength ; 1 ) ; DMD = Dep * -1 ; DArea = Lat * DMD ]; DArea )//endInnerLet )//endIf )//endLet
 Then copy & paste into FileMaker Advanced's Edit Custom Function window.