determine if field is to be calculated base on position and charge code

What I ended up with works but is different from what my original post suggest. Originally the charge code for the field I'm working with were part of a drop down. But I ended up making an area for this script static and removed it from the drop down list. Thanks goes to try67​ for his guidance to getting me to my goal. It can likely be cleaned up a little but it works.

function Calc2(ndays, nrates) {

    var travelDay = 0.75;

    for (var arrDays=ndays.length-1; arrDays>=0; arrDays--) {

        var f = this.getField(ndays[arrDays]);

        if (f.valueAsString=="") ndays.splice(arrDays, 1);

        var g = this.getField(nrates[arrDays]);

        if (g.valueAsString=="") nrates.splice(arrDays, 1);

    }

    if (ndays.length <= 0 || nrates.length <= 0)event.value = "";

    if (ndays.length == 1 && nrates.length == 1){

        var days = this.getField(ndays[0]);

        var tDays = days.value;

        if (tDays == 1){

            cdays = tDays * travelDay;

            event.value = cdays;

        }

        else if (tDays == 2){

            cDays = (tDays * travelDay) * 2;

            event.value = cDays;

        }

        else if (tDays >= 3){

            var oDays = tDays-2;

            var rates = this.getField(nrates[0]).value;

            var calcRate = oDays * rates;

            var calcFLDay = (2 * rates) * travelDay;

            event.value = calcRate+calcFLDay;

        }

    }

    if (ndays.length >= 2 && nrates.length >= 2){

        var FirstDay = this.getField(nrates[0]).value;

        var LastDay = this.getField(nrates[nrates.length-1]).value;

        var travelRate = (FirstDay+LastDay)*travelDay;

        var iFirst = this.getField(ndays[0]).value -1;

        var iLast = this.getField(ndays[ndays.length-1]).value -1;

        travelRate += iFirst * this.getField(nrates[0]).value;

        if (ndays.length > 2) travelRate += this.getField(ndays[1]).value * this.getField(nrates[1]).value;

        travelRate += iLast * this.getField(nrates[ndays.length-1]).value;

        event.value = travelRate;

    }

}