End Tick

I tried this, but sometimes the end tick result is lower than the start tick....?
What am I doing wrong?

function getEndTick(cursor)
{
// Run through all notes to get the last tick.
var endTick = 0;

console.log("getEndTick() : NStaves["+curScore.nstaves+"].");
for (var staff = 0; staff < curScore.nstaves; staff++)
{
console.log("getEndTick() : Staff["+staff+"].");
for (var v = 0; v < 4; v++)
{
cursor.rewind(0);
cursor.voice = v
cursor.staffIdx = staff;

while (cursor.segment)
{
console.log("getEndTick() : Segment.");
if(cursor.element){console.log("getEndTick() : Element["+cursor.element.type+"].")}
if (cursor.element && cursor.element.type == Element.CHORD)
{
console.log("getEndTick() : CursorTick["+cursor.tick+"] duration["+cursor.element.duration+"] = ["+(cursor.tick+cursor.element.duration)+"].");
var chordTickEnd = cursor.tick + cursor.element.duration;
if(chordTickEnd > endTick)
{
endTick = chordTickEnd;
}
}
cursor.next();
}
}
}
return(endTick);
}