TextMeasure not working as expected

I would think that this code would return "Too Verbose!" but it does not. What am I doing wrong?

var tm = new FusionProTextMeasure;
var frameWidth = 8; // 8 inches
tm.pointSize = 16000; // 160 points
tm.font = "Helvetica";
tm.useTags = false;
tm.CalculateTextExtent("Why is this not working for me in FP 8.2.7?");

var myWidth = tm.textWidth;

if (myWidth < frameWidth * 7200) result = "Nice.";
else result = "Too Verbose!";

return result;

Does it work at composition time?

Nope. I seem to be in the same boat Hadrian had. tm.textWidth always returns as "0" so long values overflow frame.