Field Not Updating

var d will not update when I change var f unless. Initially it works but any changes made to var f will not update var d. Thanks in advance for any help.

var f = Number(this.getField("Text2").value);
var d = (f * 60 + 1440);
var s = this.getField("STOPDATE").valueAsString;
var t = this.getField("Time3").valueAsString;
if ((s=="")||(t==""))event.value = "";
else event.value = d;