function bpmCalc() {
var SLen = document.getElementById("TempoCalc").SampleLength.value;
var SRat = document.getElementById("TempoCalc").SampleRate.value;
var NumBeats = document.getElementById("TempoCalc").Beats.value;

if ((SLen==0) || isNaN(SLen) || (SRat==0) || isNaN(SRat) || (NumBeats==0) || isNaN(NumBeats)) // fields are blank or non-numeric
{ 
alert("Please enter a valid sample duration, rate, and number of beats."); 
document.getElementById("TempoCalc").SampleLength.value = "";
document.getElementById("TempoCalc").SampleRate.value = "";
document.getElementById("TempoCalc").Beats.value = "";
document.getElementById("TempoCalc").Tempo.value = "";
return;
}

var SussItOut = eval(6000 * SRat * NumBeats / SLen); 
var TheTempo = "" + Math.round(SussItOut); // convert total to a string so we can fix # of digits
var dec_point=TheTempo.length-2; 
var first_part=TheTempo.substring(0,dec_point); 
var second_part=TheTempo.substring(dec_point,TheTempo.length); 
var result=first_part+"."+second_part; 
document.getElementById("TempoCalc").Tempo.value = result;
}