var max_units = 1; // quantities in excess of max_units all have the same unit price
var currency = "$"; // currency sign used in 'formatMessage()'
// Edit this function to reflect your discount prices! 
function getDiscountPrice4(units) {
// Note: It is important to work your way down from max to min amounts!
if (units >= max_units) return 1000; 
if (units <= 0) return 0;
}
function getNumberOfUnits4() {
var units = document.calculator.units4.value; 
return (units == "") ? 0 : units;
}
function showResult4(result) {
// adjust the following line if result must popup somewhere else
document.calculator.respons4.value = result;	
}
function formatMessage4(units, unit_price) {
return formatPrice4(units * unit_price);
}
// AltUnits (alternate units): add extra units to reach minimum for next discount price
function getAltUnits4(units) {
var discount_price = getDiscountPrice4(units);
if (units < max_units) do { units++ } while (discount_price == getDiscountPrice4(units));
return units;
}
function findPrice4() {
var units = getNumberOfUnits4();
var unit_price = getDiscountPrice4(units);
var alt_units = getAltUnits4(units);
var alt_unit_price = getDiscountPrice4(alt_units);
var result;
if ((units * unit_price) < (alt_units * alt_unit_price)) 
result = formatMessage4(units, unit_price); 
else
result = formatMessage4(alt_units, alt_unit_price);
showResult4(result);
}
function formatPrice4(value) {
var result= Math.floor(value) + ".";
var cents = 100 * (value-Math.floor(value)) + 0.5;
result += Math.floor(cents / 10);
result += Math.floor(cents % 10);
return result;
}
function filterNonNumeric4(field) {
var result = new String();
var numbers = "0123456789";
var chars = field.value.split(""); // create array 
for (i = 0; i < chars.length; i++) {
if (numbers.indexOf(chars[i]) != -1) result += chars[i];
}
if (field.value != result) field.value = result;
}