What if we input onclick values in array, and subtract a index from the previous index
var val1 = +$('#nssale', $parent).val();
var val2 = +$('#coogs', $parent).val();
arr.push({
"nssale" : val1,
"coogs" : val2,
});
var formula;
var formula1;
for (var i = 0; i < arr.length; i++) {
//arr[i]
formula = parseFloat(((arr[i].nssale - arr[i].coogs / arr[i].nssale)) * 100 + '%');
formula1 = parseFloat((arr[i].nssale - (arr[arr.length-2].nssale)) + '%');
}
$('#numb', $parent).val(formula.toFixed(4) + '%');
$('#differenced', $parent).val(formula1.toFixed(4) + '%');