function cost(form) {
 YourService = form.service.options[form.service.selectedIndex].value;
 YourPieces = form.pieces.value;
 YourSizes  = form.sizes.value;

//if (form.service.selectedIndex==12 && pieces < 7) {alert("Please select a minimum of 7 pieces.")}
//else {if (form.service.selectedIndex==10 && pieces < 7) {alert("Please select a minimum of 7 pieces.")}
//else {if (form.service.selectedIndex==5 && pieces < 10) {alert("Please select a minimum of 10 pieces.")};
//else
{form.yourcost.value = Math.round(YourService * YourPieces * YourSizes)};
}