function riaacalc()
{
var a3 = parseFloat(document.RIAA.A3.value);
var a4 = parseFloat(document.RIAA.A4.value);
var a5 = parseFloat(document.RIAA.A5.value);
var f1 = parseFloat(document.RIAA.F1.value);
//test input
if ((a3 == 0) || (isNaN(a3))) NotNumber();
if ((a4 == 0) || (isNaN(a4))) NotNumber();
if ((a5 == 0) || (isNaN(a5))) NotNumber();
if ((f1 == 0) || (isNaN(f1))) NotNumber();
//compute time in uS
var b3 = (1 / (a3 * Math.PI * 2)) * 1000000 ;
var b4 = (1 / (a4 * Math.PI * 2)) * 1000000 ;
var b5 = (1 / (a5 * Math.PI * 2)) * 1000000 ;
var c3 = f1 / (((b3 - b4) * (b4 - b5)) / Math.pow(b4,2));
var d3 = b4 / c3;
var e3 = ((b3 * b5)/b4)/f1;
// convert to string
var subb3 = b3 + "";
var subb4 = b4 + "";
var subb5 = b5 + "";
var subc3 = c3 + "";
var subd3 = d3 + "";
var sube3 = e3 + ""; 

//truncate string to 6 positions and display.
document.RIAA.B3.value = subb3.substring(0,6);
document.RIAA.B4.value = subb4.substring(0,6);
document.RIAA.B5.value = subb5.substring(0,6);
//
document.RIAA.C3.value = subc3.substring(0,8);
document.RIAA.D3.value = subd3.substring(0,8);
document.RIAA.E3.value = sube3.substring(0,8);
}
function NotNumber()
{
alert("Input must be a number > 0");
return;
}