Standard & Poor’s, a municipal credit rating agency, last month affirmed Andover’s AAA bond rating. The AAA rating is the highest credit rating attainable, putting Andover in the top 10 percent of Massachusetts municipalities. A town’s credit rating determines the interest rate at which the town is allowed to borrow money. The AAA rating enables the town to continue to borrow at the lowest interest rates available in the municipal marketplace. Most recently, the town received a net interest rate of 0.1399 percent on its sale of $12 million notes. Standard and Poor’s said Andover’s AAA rating reflects several factors, including very strong management with sustainable formalized policies and a consistent ability to maintain balanced budgets; strong budgetary performance; and the town’s low direct debt.