// JavaScript Document
function roundNumber(rnum, rlength) 
{ // Arguments: number to round, number of decimal places
	var newnumber = Math.round(rnum*Math.pow(10,rlength))/Math.pow(10,rlength);
	return newnumber;
}

function calculate()
{
	<!-- first -->
	var sales_1 = Number(document.getElementById("sales_1").value);
	
	var puchases_1 = Number(document.getElementById("purchases_1").value);
	
	var gross_profit_1 = 0;
	
	gross_profit_1 = gross_profit_1 + (sales_1 - puchases_1);
	
	document.getElementById("gross_profit_1").value = gross_profit_1;
	
	gross_profit_percent = roundNumber((gross_profit_1 / sales_1) * 100,2);
	
	document.getElementById("gross_profit_percent_1").value = gross_profit_percent;
	
	var bank_interest_1 = Number(document.getElementById("bank_interest_1").value);
	
	var bank_interest_result_1 = bank_interest_1 + gross_profit_1;
	
	document.getElementById("bank_interest_result_1").value = bank_interest_result_1;
	
	var total_overheads_1 = 0;
	
	total_overheads_1 = Number(document.getElementById("wages_1").value) + 
						Number(document.getElementById("use_of_home_1").value) + 
						Number(document.getElementById("insurance_1").value);
	
	document.getElementById("total_overheads_1").value = total_overheads_1;
	
	var net_profit_1 = bank_interest_result_1 - total_overheads_1;
	
	document.getElementById("net_profit_1").value = net_profit_1;
	
	<!-- second -->
	
	var sales_2 = Number(document.getElementById("sales_2").value);
	
	var puchases_2 = Number(document.getElementById("purchases_2").value);
	
	var gross_profit_2 = 0;
	
	gross_profit_2 = gross_profit_2 + (sales_2 - puchases_2);
	
	document.getElementById("gross_profit_2").value = gross_profit_2;
	
	gross_profit_percent = roundNumber((gross_profit_2 / sales_2) * 100,2);
	
	document.getElementById("gross_profit_percent_2").value = gross_profit_percent;
	
	var bank_interest_2 = Number(document.getElementById("bank_interest_2").value);
	
	var bank_interest_result_2 = bank_interest_2 + gross_profit_2;
	
	document.getElementById("bank_interest_result_2").value = bank_interest_result_2;
	
	var total_overheads_2 = 0;
	
	total_overheads_2 = Number(document.getElementById("wages_2").value) + 
						Number(document.getElementById("use_of_home_2").value) + 
						Number(document.getElementById("insurance_2").value);
	
	document.getElementById("total_overheads_2").value = total_overheads_2;
	
	var net_profit_2 = bank_interest_result_2 - total_overheads_2;
	
	document.getElementById("net_profit_2").value = net_profit_2;
}