Display blank when there is no number inputs.

i have 3 fields that need to subtract.
i tried this script. it works well, but i want "balance" field to display a value even if the value comes out ZERO.
AND the default value of balance field should be the blank. That means if there is no inputs(blank) in those three fields, 'balance' field should be the blank or hidden.
thank you!

var j = this.getField("TCA");
var i = this.getField("PPA");
var l = this.getField("SUMMARY");
event.value = j.value - i.value - l.value ;

var v = this.getField("balance");
var theValue = v.value;
if (isNaN(theValue) || (theValue < 0.005)){
v.display = display.hidden;
}
else{
v.display = display.visible;
}